Cutshort logo
A reputed firm providing world-class consulting & implementa logo
Senior Software Engineer Frontend
A reputed firm providing world-class consulting & implementa
Senior Software Engineer Frontend
A reputed firm providing world-class consulting & implementa's logo

Senior Software Engineer Frontend

at A reputed firm providing world-class consulting & implementa

Agency job
2 - 10 yrs
₹4L - ₹15L / yr
Hyderabad, Ahmedabad
Skills
skill iconAngular (2+)
skill iconAngularJS (1.x)
Ionic
skill iconNodeJS (Node.js)
skill iconJavascript
TypeScript

What you'll do:

· Perform complex application programming activities with an emphasis on mobile development: Angular, ionic, Node, TypeScript, JavaScript, Apache Cordova, RESTful APIs and more

· Assist in the definition of system architecture and detailed solution design that are scalable and extensible

· Collaborate with Product Owners, Designers, and other engineers on different permutations to find the best solution possible

· Own the quality of code and do your own testing. Automate feature testing and contribute UI testing framework

· Become a subject matter expert for our mobile applications

· Deliver amazing solutions to production that knock everyone’s socks off

· Mentor junior developers on the team

What we’re looking for:

· Amazing technical instincts. You know how to evaluate and choose the right technology and approach for the job. You have stories you could share about what problem you thought you were solving at first, but through testing and iteration, came to solve a much bigger and better problem that resulted in positive outcomes all-around.

· A love for learning. Technology is continually evolving around us, and you want to keep up to date to ensure we are using the right tech at the right time.

· A love for working in ambiguity—and making sense of it. You can take in a lot of disparate information and find common themes, recommend clear paths forward and iterate along the way. You don’t form an opinion and sell it as if it’s gospel; this is all about being flexible, agile, dependable, and responsive in the face of many moving parts.

· Confidence, not ego. You have an ability to collaborate with others and see all sides of the coin to come to the best solution for everyone.

· Flexible and willing to accept change in priorities, as necessary

 

Preferred Qualifications:

· Proficient with Apache Cordova framework

· Built or maintained custom Cordova plugin

· Demonstrable knowledge of native coding background in iOS

· Understanding of Apple certificate and profile management

· Experience developing and deploying applications within Kubernetes based containers

· Experience in Agile and SCRUM development techniques

Read more
Users love Cutshort
Read about what our users have to say about finding their next opportunity on Cutshort.
Shubham Vishwakarma's profile image

Shubham Vishwakarma

Full Stack Developer - Averlon
I had an amazing experience. It was a delight getting interviewed via Cutshort. The entire end to end process was amazing. I would like to mention Reshika, she was just amazing wrt guiding me through the process. Thank you team.
Companies hiring on Cutshort
companies logos

Similar jobs

Pattem Digital Technologies
Monisha N
Posted by Monisha N
Bengaluru (Bangalore), Noida, Pune, Chennai, Coimbatore, Kochi (Cochin)
4 - 9 yrs
₹6L - ₹30L / yr
Adobe Experience Manager (AEM)
skill iconJava
skill iconJavascript
Apache Sling
skill iconHTML/CSS
+1 more

AEM Sites Developer


Pattem Digital Technologies is looking for a highly effective Adobe Experience manager(AEM) Developer to join our team. This person will utilize best practices and methodologies to design and implement the best solution for our clients. This key member of our team contributes to the entire software development lifecycle including analysis, requirement specification, use case and data modeling, technical design, development, testing, and implementation. This individual will be focused on delivering assigned tasks and/or specific tracks of the solution on time, escalating issues when appropriate as well as educating and leading others in the form of code reviews, workshops, and documentation.


Know your work :


  • Build and maintain solutions for AEM (Sites, Assets). 
  • Work in Agile Methodology - be part of Sprint Ceremonies, provide accurate estimates for assigned development Stories & deliver on time. 
  • Follow Best and Recommended Practices while implementing solutions. 
  • Ensure Code Quality, Readability, Maintainability and Security. 
  • Coordinate with multiple teams (Ex: UI/QA) for any dependencies. 
  • Write JUnit Test Cases for Unit Testing 
  • Communicate with customer teams on requirements effectively. 
  • Manage customer expectations of response time and issue resolution 
  • Troubleshoot and reproduce the technical problems reported by customers and define workarounds. 
  • Create and integrate content-driven applications on top of the AEM platform, and integrate with other systems.
  • The AEM Developer provides technical leadership with a focus on CMS solutions. This Includes planning, guiding the design, estimation, user interface, people management, issue resolution and quality assurance. 
  • Collaborate across disciplines and use their in-depth knowledge of AEM technology to help deliver business solutions for our clients.

What you need to apply :

  • Good understanding of UI technologies like JQuery, Java Script, HTML 5, CSS. 
  • Good understanding of backend technologies like Java EE, Servlets, JSP, Tag libraries, and JSTL skills, combined with a good understanding of Enterprise Java frameworks such as Spring, Spring Boot and Hibernate.
  • Good understanding of CI/CD tools like Maven, Jenkins. 
  • Good understanding of Code Quality and Security tools like SONAR. 
  • Good understanding of Touch UI, Sightly (HTL) and Sling Models.
  • Good understanding of AEM Backend Development like Sling Servlets, OSGi Components and JCR Queries. 
  • Solid experience in problem analysis and resolution of technical problems.
  • Ability to handle clients professionally during all interfaces. 
  • Ability to work in extended hours to overlap with North America timings. 
  • Strong written and verbal communication skills. 
  • Minimum 3+ years of experience in AEM.
  • 3-4 years of experience in CMS implementations with Adobe Experience manager(AEM).
  • Hands-on work experience on Adobe 6.x versions.
  • Knowledge in AEM foundational concepts, including the CRX repository, the AEM platform, the use of core frameworks such as Apache Sling and Apache Felix. 
  • Knowledge on latest AEM features.
Read more
Deqode
at Deqode
1 recruiter
Roshni Maji
Posted by Roshni Maji
Pan India
4 - 8 yrs
₹6L - ₹13L / yr
TypeScript
frontend

Job Title: TypeScript Developer

Location: Pan India

Company: Deqode

Mode of work: Hybrid

Experience: 4+ years

Employment Type: Full Time


About Deqode

At Deqode, we solve complex business problems using emerging technologies. We work with global clients to build innovative and scalable solutions. Join our team to be part of a fast-paced environment that encourages continuous learning and growth.


Job Summary

We are looking for a skilled TypeScript Developer to join our development team. You’ll be responsible for building scalable and maintainable applications using TypeScript, collaborating with cross-functional teams, and contributing to the full software development lifecycle.


Key Responsibilities

  • Develop and maintain web applications using TypeScript and modern frameworks (e.g., React, Angular, Node.js).
  • Write clean, scalable, and well-documented code.
  • Work closely with designers, product managers, and backend developers.
  • Optimize applications for speed and scalability.
  • Perform code reviews and participate in agile development processes.
  • Stay updated with the latest trends and best practices in web development.

Requirements

  • Strong proficiency in TypeScript and JavaScript (ES6+).
  • Experience with front-end frameworks like React or Angular.
  • Familiarity with backend development using Node.js is a plus.
  • Understanding of RESTful APIs, version control (Git), and unit testing.
  • Excellent problem-solving skills and attention to detail.
  • Bachelor’s degree in Computer Science or a related field (preferred).
Read more
Top 3 Fintech Startup
Top 3 Fintech Startup
Agency job
via Jobdost by Sathish Kumar
Hyderabad, Ahmedabad
8 - 11 yrs
₹20L - ₹35L / yr
skill iconAngularJS (1.x)
skill iconAngular (2+)
Ionic
Apache Cordova
skill iconNodeJS (Node.js)
+4 more

Job Description

 

Job Location - Hyderabad & Ahmedabad

 

What you'll do:

· Perform complex application programming activities with an emphasis on mobile development: Angular, ionic, Node, TypeScript, JavaScript, Apache Cordova, RESTful APIs and more

· Assist in the definition of system architecture and detailed solution design that are scalable and extensible

· Collaborate with Product Owners, Designers, and other engineers on different permutations to find the best solution possible

· Own the quality of code and do your own testing. Automate feature testing and contribute UI testing framework

· Become a subject matter expert for our mobile applications

· Deliver amazing solutions to production that knock everyone’s socks off

· Mentor junior developers on the team

 

What we’re looking for:

· Amazing technical instincts. You know how to evaluate and choose the right technology and approach for the job. You have stories you could share about what problem you thought you were solving at first, but through testing and iteration, came to solve a much bigger and better problem that resulted in positive outcomes all-around.

· A love for learning. Technology is continually evolving around us, and you want to keep up to date to ensure we are using the right tech at the right time.

· A love for working in ambiguity—and making sense of it. You can take in a lot of disparate information and find common themes, recommend clear paths forward and iterate along the way. You don’t form an opinion and sell it as if it’s gospel; this is all about being flexible, agile, dependable, and responsive in the face of many moving parts.

· Confidence, not ego. You have an ability to collaborate with others and see all sides of the coin to come to the best solution for everyone.

· Flexible and willing to accept change in priorities, as necessary

 

Preferred Qualifications:

· Proficient with Apache Cordova framework

· Built or maintained custom Cordova plugin

· Demonstrable knowledge of native coding background in iOS

· Understanding of Apple certificate and profile management

· Experience developing and deploying applications within Kubernetes based containers

· Experience in Agile and SCRUM development techniques

Read more
primathonin
at primathonin
2 recruiters
Sagar Patidar
Posted by Sagar Patidar
Gurugram, Indore
3 - 5 yrs
₹8L - ₹12L / yr
skill iconReact.js
skill iconJavascript
skill iconRedux/Flux
skill iconHTML/CSS

Responsibilities:

  • Review, Evaluate, and Validate technical requirements.
  • Work and lead other team members to translate the requirements into final deliverables.
  • Understand Storyboards and Visual mock-ups.
  • Understand and utilize the latest tools, technologies, and trends in Web development.
  • Ensure the deliverables meet Primathon standards, and guidelines.
  • Developing your frontend capability in complex problems and expanding your horizon of technologies.
  • Responsible for designing, coding and modifying web pages that are focused on content within the standards, guidelines and requirements of clients.
  • Work with clients, and other team members as appropriate.
  • Understand and utilise the tools and technologies being used.
  • Work with CTO to keep on track with the project plan.
  • Come up with efficient, modular and scalable solutions for business and technical problems.


Requirements:

  • Experience with Frontend technologies (React.js ).
  • Proficient understanding of web markups, including HTML, CSS-3
  • Proficient with modern JavaScript (ES6+: classes, modules, arrow function, destructuring etc).


Read more
technology based supply chain management
technology based supply chain management
Agency job
via Hunt & Badge Consulting Pvt Ltd by Chandramohan Subramanian
Chennai
3 - 7 yrs
₹10L - ₹20L / yr
skill iconAngularJS (1.x)
skill iconReact.js
User Interface (UI) Development
skill iconJavascript
Experience converting visual designs to HTML with an acute eye for detail and design fidelity
• Strong understanding of GUI architecture, site navigation and web design principles, and the ability to create and maintain web pages quickly and efficiently
• Extensive web programming experience including web security, cross browser compatibility, and performance tuning
• Development experience in the area of: Responsive design/development and mobile device applications and optimized Web sites
• Hands on design & development skills in HTML/XHTML, HTML5, CSS2, CSS3
• Knowledge of W3C standards, Web accessibility
• Hands on experience with Object oriented JavaScript and Design Patterns
• Extensive experience in at least one of the modern frameworks like jQuery / jQueryUI / Angular JS / ExtJS / Ember JS / Backbone JS / React / TypeScript
Read more
FinTech Start Up
FinTech Start Up
Agency job
via IndependentConsultant by Melrose Pinto
Pune
6 - 10 yrs
₹18L - ₹22L / yr
skill iconReact.js
TypeScript
skill iconRedux/Flux
react
skill iconJavascript
+1 more
We are looking for talented individuals to quickly grow our Engineering Center based in Pune(India). If you are a smart, passionate, hardworking, team oriented, creative thinker, we promise you an amazing environment in which to spread your wings, participate in solving a complex technical problem and creating a brand-spanking new product to solve a problem faced by every company worldwide. 

Job Description :

- We are a Fintech Company based in Pune, a B2B Trade Digitization platform for SMEs and Corporates to collaborate and work with Financial Institutions to raise short term fundings for payables and receivables financing.

- We are thus well placed to help Corporates and their Supply Chains to meet their GST needs.

Technologies
The platform is built using a polygot technology stack:
● Platform Backend: JVM
● Web Layer: ReactJS and related ecosystem, HTML, Javascript, CSS, Bootstrap
● API & Business Layer: Kotlin and functional programming
● Client Apps and Customer Integrations: Kotlin, Jersey ReST Framework, home
grown optimized HTTP and SQL libraries
● Mobile Apps: Android, iOS
● Database: MySQL
○ JVM – Hibernate & Exposed as ORM library
○ Python – SQLAlchemy as ORM library
● Build Tools: Gradle, Shell Scripting, AWS Code Build, Jenkins
● Ops Automation: Ansible, Terraform
● Servers: Ubuntu Linux
● Version Control: GIT
● Test Automation: Python - unittest, pyhamcrest, freshen, nose. JVM – Junit,
Kotlin Test
● Cloud Providers: Amazon AWS, Linode

Requirements
We are a self organized engineering team with a passion for programming and solving
business problems for our customers. We are looking to add a Senior UI Developer in
our team having hands-on technical experience of 6+ years. We encourage our team to
continuously learn new technologies and apply the learnings in the day to day work
even if the new technologies are not adopted. We strive to continuously improve our
practices and expertise to form a solid backbone for the product, customer relationships
and sales teams which enables them to add new customers every week to our financing
network.

As an engineering team member, you will
● Work collaboratively with product, customer support and DevOps team to build,
enhance, maintain, deploy and operate our systems.
● Continuously automate operational processes to improve efficiencies and
productivity and enhance customer experience
● Work closely with the architect to continuously refactor the system architecture
and design to meet the changing landscape triggered by technology changes
and business growth
● Work with the DevOps team to build and maintain tools for deployment,
monitoring and operations.
● Ensure that development processes and deliverables always adhere to the
mandates laid down for for various certifications (PCI and ISO 27001 in
particular)

Skills required
● Pre-requisites: Hands on experience in ReactJS and Redux. Experience in
typescript will be an additional benefit.
● Should be passionate about technology and ready to deep dive into
programming .
● Should have sound expertise of writing testable code and appreciate defect free
coding.
● Should be able to reason/argue/discuss/suggest solutions and alternatives.
● Should be able to decipher the core problem to be solved during discussions
with product team and/or customers
● Should have good communication skills and experience working in teams
● Experience of working in financial domain will help but not a necessity
Read more
Hexaware Technologies
Agency job
via telamonhr by Akanksha Saxena
Mumbai, Chennai, Pune, Bengaluru (Bangalore)
1 - 3 yrs
₹9L - ₹10L / yr
skill iconAngularJS (1.x)
skill iconReact.js
TypeScript
Ember.js
skill iconPython
+9 more

1.       Strong knowledge in Front end scripting like EJS, JavaScript, Jquery

 

2.       Proficiency with fundamental front-end languages such as HTML, CSS.

 

3.       Familiarity with JavaScript frameworks such as Angular JS, React, and Amber.

 

4.       Proficiency with server-side languages such as Python / Ruby / Java / PHP/ .Net

 

5.       Good Understand with database technology such as MySQL, Oracle, and MongoDB.

Read more
NA
NA
Agency job
via Promotup HR Solutions by Shivani Shembekar
Ahmedabad
2 - 4 yrs
₹6L - ₹7L / yr
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconJavascript
skill iconHTML/CSS
skill iconjQuery
+3 more

We are looking for an Angular Developer to join our awesome team and deliver a streamlined user experience. We want a team member who strives to develop a first class codebase using Angular best practices. As an Angular 6/7/8 Developer, you will implement a complete user interface in the form of a mobile and desktop web app.

 

AngularJS Developer duties and responsibilities:

  • Develop User interfaces for Modern Rich Internet Applications with the latest Front End Technologies
  • Perform product analysis and development tasks of increasingly complex nature which may require extensive research and analysis.
  • Writing tested and documented JavaScript, HTML and CSS
  • Make design and technical decisions for Angular projects.
  • Develop application code and unit test in the Angular, Rest Web Services and Java technologies for the Application Development Center.
  • Ensuring high performance

 

AngularJS Developer requirements and qualifications:

  • Up to 3 years Experience with Angular 6/7/8.
  • Strong expertise with HTML, CSS, and writing cross-browser compatible code.
  • Good understanding of AJAX and JavaScript Dom manipulation Techniques
  • Experience with RESTful services
  • Experience in JavaScript build tools like grunt or gulp
  • Expert in any one of the modern JavaScript MV-VM/MVC frameworks (Angular, JQuery, NodeJS, GruntJS)
  • Familiar with testing frameworks (Ex. Jasmine)
  • Test runner framework (Ex. Karma)
  • Hand on and implements complex Angular applications, directives, controllers, services
  • Critical thinker and problem-solving skills
  • Team player
  • Good time-management skills
  • Great interpersonal and communication skills

 

 

Pre-requisites:

 

  • Excellent English communication skills
  • Should be willing to run that extra mile for the role
  • A positive approach with a go-getter attitude.
  • Excellent team player
Read more
Innovura Technologies Private Limited
Remote, Ahmedabad, Vadodara, Mumbai
2 - 6 yrs
₹3L - ₹6L / yr
react
skill iconReact.js
skill iconJavascript
skill iconHTML/CSS
User Interface (UI) Design
  • We are looking for a skilled React.js Developer to join our front-end development team. In this role, you will be responsible for developing and implementing user interface components using React.js concepts and workflows such as Redux, Flux, and Webpack. You will also be responsible for profiling and improving front-end performance and documenting our front-end codebase.
  • To ensure success as a React.js Developer, you should have in-depth knowledge of JavaScript and React concepts, excellent front-end coding skills, and a good understanding of progressive web applications. Ultimately, a top-class React.js Developer should be able to design and build modern user interface components to enhance application performance.
 

React.js Developer Responsibilities:

  • Meeting with the development team to discuss user interface ideas and applications.
  • Reviewing application requirements and interface designs.
  • Identifying web-based user interactions.
  • Developing and implementing highly-responsive user interface components using React concepts.
  • Writing application interface codes using JavaScript following React.js workflows.
  • Troubleshooting interface software and debugging application codes.
  • Developing and implementing front-end architecture to support user interface concepts.
  • Monitoring and improving front-end performance.
  • Documenting application changes and developing updates.

React.js Developer Requirements:

  • Bachelor’s degree in Computer Science, Information Technology, or a similar field.
  • Previous experience working as a React.js Developer.
  • In-depth knowledge of JavaScript, CSS, HTML and front-end languages.
  • Knowledge of REACT tools including React.js, Webpack, Enzyme, Redux, and Flux.
  • Experience with user interface design.
  • Knowledge of performance testing frameworks including Mocha and Jest.
  • Experience with browser-based debugging and performance testing software.
  • Excellent troubleshooting skills.
  • Good project management skills.
Read more
Peppo Technologies Private Limited
Rukhsana Aziz
Posted by Rukhsana Aziz
Remote, Bengaluru (Bangalore)
2 - 5 yrs
₹6L - ₹15L / yr
skill iconJavascript
skill iconReact.js
skill iconAngularJS (1.x)
skill iconVue.js
Ember.js
+3 more

Peppo is a fair food ordering utility. It helps restaurants manage both the demand and the delivery sides of their business, on the cloud.

 

Peppo is a seed funded startup, developed by the team at First WalkIn Technologies. Founded in 2015, our incredible team of engineers, programmers, designers, data scientists and marketing experts have worked tirelessly to bring digital transformation solutions to iconic F&B brands such as Cafe Coffee Day, McDonald's, Pizza Hut and Domino's.

 

Now we've set out to bring the same expertise to all restaurants, big and small, so they can compete on fair terms in an increasingly digital world.

 

About Role

 

We are looking for an experienced Front-end Software Engineer with first-rate programming skills to join our retail platform team. In this role, you’ll be making some of the most significant decisions for the company. You need to have strong problem solving capabilities, be a team player and have great communication skills. You also need to be goal-oriented, have the ability to understand the core architecture and take  up responsibility of product feature development. You must be a highly technical, hands-on developer with passion for producing high standard and robust code.

 

  • Collaborate with the design/business teams and develop software meeting product requirements, with lead responsibility for different features in the product.
  • Responsible for communicating and reporting to the tech lead.
  • Code new features as well as maintain existing features.
  • Participate in technical design and architecture reviews.
  • Write technical documentation.
  • Participate in code reviews.
  • Prototype and/or redesign features.
  • Fix bugs.

 

We offer a friendly, casual, collaborative working environment that is mission-driven and results-oriented. Our small office is in a great space in Bangalore. Due to the COVID situation, we are committed to having a fully remote engagement.

 

Skills and Requirements

We are looking at your experience not just in terms of the years you’ve clocked but the aptitude to get things done. Here’s the skills that your job would entail, so please make sure you highlight the following in any capacity you have demonstrated - professional, freelance or hobbyist.

 

  • Good to have an overall 3+ years of software development experience.
  • Strong proficiency in modern JavaScript.
  • Expertise with modern JS libraries/frameworks at least one of these JS frameworks - React.JS, Vue, AngularJS, NextJS
  • Experience with testing frameworks, practices and processes.
  • Demonstrated skills in developing, releasing, and maintaining high quality web applications.
  • Solid experience on REST APIs, JSON, Test Driven Development (TDD) and standards.
  • Good communication skills and ability to work independently or in a team.
  • GraphQL experience is an added bonus

 

Job Perks

  • Small team with an opportunity to have a steep learning curve. 
  • Have a meaningful impact on end customers and sellers on their experience with digital tools.
  • Work on redefining the e-commerce experience by building cooperatives for the micro-services era. This makes Peppo a perfect home for those looking to pursue compassionate capitalism.
  • Train under a diverse and accomplished set of team leads, mentors and investors who have worked in government and big tech.
  • Holistic development guaranteed as you will grow in an environment that prizes lateral thinking allowing you to supplement your core responsibilities with additional functions.
  • Competitive compensation and flexibility to work from anywhere since Peppo uses the best of productivity tools.

 

Our Preferred Resume Format

  • Polished resume with list of projects clearly listed (with responsibilities you held)
  • Links to interesting projects that you worked on (professional, freelance or hobbyist)
  • Blogs written and any other public contributions you made

 

Our Interview Process

  1. Resume evaluation: We will screen all incoming CVs and invite candidates for next round, fitting our job profile description.
  2. Case study: If you are one of the shortlisted candidates, you will be sent a case study to solve.
  3. Phone screening: we will follow up with a phone screening round for better understanding of the CV, technical proficiency, experience etc.
  4. F2F Round(s): The next round is a direct face-to-face discussion over a video call.

 

Peppo is an equal opportunity employer. We're excited to work with talented and empathetic people no matter their race, caste, color, gender, sexual orientation, religion, national origin, physical disability, mental well-being, or age. Our code of conduct reflects the kind of company we strive to be, and we celebrate our diversity for that truly makes us create products that cater to the world.

 

Here’s a few resources for you to understand Peppo landscape:

 

The simplest way to think of Peppo is that it is a backend for restaurants that takes them online, not on just one channel but on all of them. App publishers that integrate with Peppo, will see every restaurant that uses Peppo and can enable food ordering through their own front-end. On the fulfilment side, Peppo allows restaurants to plug into an aggregated delivery fleet on which it helps restaurants choose between various providers to optimise between delivery costs and performance. Read more about:

 

 
Read more
Why apply to jobs via Cutshort
people_solving_puzzle
Personalized job matches
Stop wasting time. Get matched with jobs that meet your skills, aspirations and preferences.
people_verifying_people
Verified hiring teams
See actual hiring teams, find common social connections or connect with them directly. No 3rd party agencies here.
ai_chip
Move faster with AI
We use AI to get you faster responses, recommendations and unmatched user experience.
21,01,133
Matches delivered
37,12,187
Network size
15,000
Companies hiring
Did not find a job you were looking for?
icon
Search for relevant jobs from 10000+ companies such as Google, Amazon & Uber actively hiring on Cutshort.
companies logo
companies logo
companies logo
companies logo
companies logo
Get to hear about interesting companies hiring right now
Company logo
Company logo
Company logo
Company logo
Company logo
Linkedin iconFollow Cutshort
Users love Cutshort
Read about what our users have to say about finding their next opportunity on Cutshort.
Shubham Vishwakarma's profile image

Shubham Vishwakarma

Full Stack Developer - Averlon
I had an amazing experience. It was a delight getting interviewed via Cutshort. The entire end to end process was amazing. I would like to mention Reshika, she was just amazing wrt guiding me through the process. Thank you team.
Companies hiring on Cutshort
companies logos