Cutshort logo
Mobile Programming LLC logo
Software Developer
Mobile Programming LLC's logo

Software Developer

Prateek Kaushik's profile picture
Posted by Prateek Kaushik
3 - 7 yrs
₹6L - ₹11L / yr
Pune
Skills
skill iconNodeJS (Node.js)
skill iconAngular (2+)
skill iconJavascript
Object Oriented Programming (OOPs)
Cloud Computing
skill iconHTML/CSS
Web Development
Bachelor’s degree in computer science, engineering or related field. 2+ years of experience developing web applications 2+ Experience in one or more of technologies such as Angular, HTML5 Nice To Have Full-stack development Experience with one or more cloud platform Knowledge of containerization technologies. Responsibility Develop cloud application for Manufacturing Process Simulation Independent, creative and self-motivated team player with passion for constant learning and change Key Skills Primary Skills Node.JsCloudAngularHTML Secondary Skills Desired Profile Education BE
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

About Mobile Programming LLC

Founded :
1998
Type :
Services
Size :
1000-5000
Stage :
Profitable

About

Mobile programming LLC is a US based MNC company. Our services are focused on Mobility Solutions, Custom App Development, Cloud Solutions, IoT, AR/VR, Blockchain, Artificial Intelligence & Machine Learning, Predictive Analytics & Big Data Solutions, and several other trending as well as emerging technologies.

You can find more details on - https://www.mobileprogramming.com/

Read more

Company video

Mobile Programming LLC's video section
Mobile Programming LLC's video section

Connect with the team

Profile picture
Chandni oli
Profile picture
Piyush Singla
Profile picture
Vandana Dhiman
Profile picture
Abha Sharma
Profile picture
Krishna sravani
Profile picture
Neha Rana
Profile picture
Abhinav Dang
Profile picture
Preeti Gupta
Profile picture
Garima Walia
Profile picture
Surya Prabha
Profile picture
Preeti Bedi
Profile picture
Navrose Kaur
Profile picture
Nivedita Kumari
Profile picture
Anurodh Dhanwik
Profile picture
nitika nitika
Profile picture
Pankaj Bhardwaj
Profile picture
Tripti Jaiswal
Profile picture
Apurva kalsotra
Profile picture
Shweta Verma
Profile picture
Priyanka Anbarasu
Profile picture
Sindhuja Pasupathi
Profile picture
Surabhi Parihar
Profile picture
Simran Saini
Profile picture
Jagdeep Kaur
Profile picture
Sheetal Sharma
Profile picture
Divya Joshi
Profile picture
Nishanth Lingaraj
Profile picture
Prateek Kaushik
Profile picture
sudiksha arora
Profile picture
Zareen Kareem
Profile picture
Ragu Badri
Profile picture
vandana chauhan
Profile picture
Abha Sharma
Profile picture
Vinay Sattu

Company social profiles

N/A

Similar jobs

Sprinto
at Sprinto
2 recruiters
Jasmeet Dhillon
Posted by Jasmeet Dhillon
Remote only
2 - 8 yrs
₹15L - ₹30L / yr
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconReact.js
skill iconNodeJS (Node.js)
skill iconNextJs (Next.js)
+2 more
What is Sprinto?
 
Sprinto is an early-stage SaaS startup, working in the information security "compliance" space. This is a flourishing area but has not seen any innovation in the last couple of decades. Thanks to some macro-changes, we think the space is ripe for a startup to become a market leader. Our job as founders and founding engineers is to ensure that Sprinto has a shot at this opportunity.
 
Why work with us?
 
Sprinto has an experienced founding team. Prior to Sprinto, we (http://girishredekar.net/">Girish and https://www.linkedin.com/in/raghuveerkancherla">Raghu) built http://recruiterbox.com/">Recruiterbox.com. We bootstrapped the recruiter box from 2011 to 2017 and scaled it to 2500+ global customers and a team of ~45 people spread across India and the US. At the end of 2017, Recruiterbox was acquired by Turn/River capital.
 
We wrote most of the early code at Recruiterbox and remained among the top 5 committers even when the company ran at scale. We program because we love to, and understand the importance of good programming practices. At Recruiterbox, we adopted practices like writing unit tests, integration tests, CI, CD very early in our journey.
 
We believe good engineering breeds good results - rapid development, low tech debt, easy maintainability, etc. Our current choice of tech stack can be an interesting point of conversation when we meet.
 
Sprinto is well-capitalized by top-notch investors like Elevation, Accel and Blume. While you have all the advantages of working on challenging problems that come with working in a startup, you also don't have the risk of the company running out of money.
 
You will get to work with seasoned programmers who care about their craft and engineering culture
 
Last but not the least, stock options. While all early-stage startups offer stock options, not all of them are the same. At Sprinto, we aren't satisfied with being just a large/successful company. We want to be the category leader. On a good outcome, your stint with Sprinto will leave you with no need to work for money and you only continue to work for passion.
 
What are we looking for?
 
You are a hands-on programmer and have professionally programmed for at least 2 years, preferably building web applications.
 
You have good problem-solving and communication skills, both spoken and written.
 
You are a quick learner and prefer picking up tools & languages as needed for solving the problem at hand in the best way possible
 
It helps if you've lived with the consequences of bad programming choices. You have an eye for spotting premature over-engineering that needlessly delays projects, but also notice when something that sounds fast/easy/tempting today will cost us severely in a few months.
 
You understand that, ultimately, Code is a means of solving the business/customer problems, and thrive in making the trade-offs that solve such problems efficiently.
Read more
Cast Software
at Cast Software
3 recruiters
Sibil Sagar
Posted by Sibil Sagar
Bengaluru (Bangalore)
3 - 6 yrs
₹10L - ₹30L / yr
skill iconReact.js
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconHTML/CSS
RESTful APIs
+4 more

Full-stack Developer

CAST is the market leader in Software Intelligence. Its unique technology thoroughly examines the structure of complex software systems, with MRI-like precision. It delivers accurate, actionable, and automated views of software architecture, critical flaws, quality grades, sizing metrics, open source usage, and cloud readiness levels. Hundreds of companies rely on CAST for greater objectivity in crucial business decisions, faster application modernization for Cloud, raising the quality and security of their custom software. CAST operates globally with offices in North America, Europe, India, China.

Title: Software Developer

Location: Bangalore

Job definition

Working at CAST R&D means being an important part of a highly-talented, fast-paced, multicultural and Agile team based in Paris (France) and Bangalore (India). The team builds sophisticated source code analysis platform leveraging parsing, control flow, data flow and others mechanisms to fully understand the inner structure of the complex IT Systems developed and used by the Fortune 500 companies.

You, working as individual contributor, will be integrated in Dashboard Teams working on web portals of CAST AIP. Your teammates will be located in India and in France and you will have the opportunity to travel to France every year.
You will collaborate to writing and designing new features and improve existing ones. You will write unit tests and drive code reviews. You will participate into best practices definition and technology watch. Depending on will, skills and experience, you will have the opportunity to take technical lead on topics or projects.

While the domain of CAST is a niche, the position will propose you to work on software that dedicate to company Dashboards and control software, focusing on technical and creative skills.

Profile

  • Experience : 3-6 years
  • Experience in developing front-end/full stack applications at scale
  • Should have experience in any of the front-end framework like React, Angular, BackboneJS, Ext etc and HTML/CSS/Bootstrap .
  • Experience in backend technologies like GOLANG, NodeJS, Python, REST web services and Java(OOPS, Collections, DB Access) or any other technology.
  • Hands on experience in JavaScript Concepts (OO-JS, Closures, Unit Testing, Module Patterns etc)
  • Good to have skills like REST, Bootstrap, UI Components, CI/CD, NoSQL based DB is added advantage.
  • Experience with advanced CSS programming using LESS or SASS is a plus.
  • Expertise in of server side technologies and SQL/NoSQL is a plus.
  • Experience of JavaScript testing frameworks like Karma, Mocha, Jest etc.
  • It involves design the software system, Select algorithms, theories or technologies that will be used for BUSINESS Applications
  • Contribute to software development design discussions for new features and new product development
  • Strong Problem solving skills and ability to troubleshoot applications & environment issues.
  • Adaptability, ability to learn faster, Independent, responsible and diligent.
  • Good team spirit and interpersonal skills, Excellent Written, Verbal, communication skills, Analytical skills & Business Thinking.

The candidate should have a passion for technology and a flexible, creative approach to problem solving. You are autonomous and take responsibility for your work.

Ideally, you know how to write unit tests and maybe even better write them in TDD. You have knowledge in agile methodologies such as Scrum. You know about GIT and the use of continuous integration tools. You have developed single page JS applications end to end.

Candidate should have a bachelor or Master technical degree or equivalent experience. Strong knowledge in software engineering. Proactive Self Starter, creative thinker in designing, developing and supporting applications. Work as part of cross functional, passionate agile project teams to ensure quality is driven into the heart of the development process.

 

Read more
Think n Solutions
at Think n Solutions
2 recruiters
TnS HR
Posted by TnS HR
Bengaluru (Bangalore)
2 - 7 yrs
Best in industry
skill iconJava
J2EE
skill iconSpring Boot
Hibernate (Java)
skill iconAngular (2+)
+19 more

Technical Skills Desired:

 

  • Must have experience in either of JavaScript frameworks: Angular
  • Must have experience in either of backend software development [J2EE, Spring Boot, Spring core, JPA]
  • Must have experience in designing/implementing Hibernate/ORM, Restful web services, Micro Services using Java
  • Knowledge with relational/ NoSQL databases (e.g., Oracle, MySQL, MongoDB)
  • Knowledge with versioning (Git or SVN) /build tools (Maven/Ant/Gradle/Junit), Unit testing & code coverage tools is desired
  • Knowledge of App / Web servers (NGINX / Tomcat / Jboss Wildfly)
  • Understands the process of new application development and has the ability to apply these concepts with minimal mentoring and supervision.
  • Advanced knowledge experience using any of IDE (e.g., Eclipse, SonarQube, STS, VS Code)
  • Knowledge on Cloud platform, technologies & deployments is an added advantage
  • Resolves technical issues through debugging, research, and
  • Must have experience with Agile tools

Functional Skills Desired:

  • Good knowledge in product development domains
  • Knowledge in Finance and Insurance domain preferred
  • Maintain quality and ensure responsiveness of
  • Complete application development by coordinating requirements, schedules, and activities contributing to team meetings;
  • Troubleshooting development and production problems across multiple environments and operating platforms.
  • Collaborate with the rest of the engineering team to design and launch new features
  • Understanding and implementation of security and data
  • Ensure designs are in compliance with specifications and standards and best industry
  • Usage of Process tools – JIRA, TFS, HP QC or any other agile tools, also knowledge of CMM Level 3 development process.
  • Self-motivated & working independently with minimal
  • Maintain code integrity and
  • Experience working with graphic designers and converting designs to visual
  • Follow the coding standards for java and angular

 

Technical Skills Good to Have:

 

  • Usage of troubleshooting tools like J Profiler, J Meter or application performance tuning
  • Exposure to Non-web-based developments, for both mobile and
  • Development experience using Docker, Kubernetes, Containerization etc in AWS or other cloud platforms
  • Willing to take up proof of concepts and showcase the technical capability
  • Usage of design tools Visio or draw io
  • Usage of CI/CD pipeline
Read more
Fintech/Investment Tech /Wealth Tech
Fintech/Investment Tech /Wealth Tech
Agency job
via Mithra Global by Dipa Anand
Remote only
1 - 4 yrs
₹7L - ₹12L / yr
skill iconNodeJS (Node.js)
skill iconExpress
Sails.js
skill iconJavascript
skill iconBackbone.js
+3 more
For our MNC client which caters to the BFSI domain

This is currently a Hybrid mode WFO from the WeWork location closest to your home/option for a permanent Remote WFH position.

Mandatory Experience: 1 to 4 years as LEAD or Overall experience of 6+ Years in Software Development

Responsibilities :

- Build reusable code and libraries for future use.

- Own & build new modules/features end-to-end independently.

- Collaborate with other team members and stakeholders.

Required Experience, skills and abilities :

- Thorough understanding of Node.js, JavaScript, its quirks, and workarounds.

- Excellence in at least one framework like StrongLoop loopback, express.js, sail.js etc.

- Excellence in at least one Javascript framework like, vue.js, Ember, React or Backbone.

- Basic architectural understanding of modern-day web applications

- Diligence for coding standards

- Must be good with git and git workflow

- Experience with external integrations is a plus

- Working knowledge of AWS, GCC, Azure

- Expertise with Linux-based systems

- Experience with CI/CD tools like Jenkins is a plus.

- Experience with testing and automation frameworks.

- Extensive understanding of RDBMS systems

Interpersonal Skills :

- Go-getter attitude and a passion for making killer web applications

- Good communication and interpersonal skills.

- Ability to work in a high-pressure environment

- Ability to quickly understand complex problems and devise effective solutions

Extra plusses(Optional) :

- Knowledge of D3/NodeJS/dash etc.

- Experience with Cloud as a platform or Infrastructure.

- Inclination to application design standards

Other Details :

Salary: Market standard with performance-linked benefits Depending upon the candidates

Industry: Financial Technology

Functional Area: BFSI
Read more
Futura Apsol Pvt Ltd
at Futura Apsol Pvt Ltd
1 video
1 recruiter
Shubhankar Ranade
Posted by Shubhankar Ranade
Pune
0 - 3 yrs
₹1L - ₹4L / yr
skill iconReact.js
skill iconNodeJS (Node.js)
skill iconHTML/CSS
skill iconRedux/Flux
SQL

We are looking for a full stack developer having expertise in web development, with experience in React, NodeJS, Postgres. Should also have experience with API development & integration.

 

Key responsibilities:

- Develop back-end components that are scalable and reusable which aligns

with the existing architecture.

- Integrate user-facing elements developed by front-end developers with server-

side logic.

- Design, build, test, and document code

- Coordinate with internal teams to understand user requirements and provide

technical solutions.

- Make architecture decisions that contribute to maintainable systems.

 

Skill(s) required:

- HTML , JavaScript , CSS , NodeJs, ReactJs, Redux, Redux Saga, Postgres, SQL,

Git

- Computer science graduates would be preferred

- Familiarity with front-end technologies (like JavaScript, HTML, Bootstrap, CSS,

and React.js)

- Basic understanding of tech stacks - Postgres & Git

- Ability to work independently is a must.

- To add new features according to the requirements, to work on regular updates

as per the latest technological advancements.

- A solid understanding of how web applications work including security, session

management

 

You will be responsible for:

- Architecting and building these applications, as well as coordinating with the

teams responsible for other layers of the product infrastructure.

- Building pixel-perfect, smooth UIs across both mobile platforms.

- Maintaining code and writing automated tests to ensure the product is of the

highest quality.

- Diagnosing and fixing bugs and performance bottlenecks for performance that

feels native.

Read more
Jointworksolutions
at Jointworksolutions
2 recruiters
Ale Sai  Preetham
Posted by Ale Sai Preetham
Remote only
5 - 10 yrs
₹3L - ₹15L / yr
Servlets
JSP
JDBC
skill iconAngularJS (1.x)
skill iconVue.js
+5 more

Requirement :- Java Tech Lead (with knowledge of Angular)

 

  • 5+ years of experience into Java 6/7/8, J2EE, EJB, Servlets, JSP, JDBC, LOG4J, JSON, XML
  • 3+ years of experience in Spring Boot, Sprint Rest, Spring MVC.
  • 5+ years of experience in REST, Micro service Development
  • Knowledge of Design Patterns (Good to Have).
  • Proven Experience in building complex web systems that have been successfully delivered to customers
  • Experience in writing SQL-queries and knowledge of PL/SQL
  • Experience in working with databases Oracle 10g, 11g, Postgres, Cassandra etc
  • Exposure/Experience in working/setting up CI and CD environments (DevOps).
  • Knowledge of development lifecycle, standards, approaches, utilities and environment: shells, version control systems, IDEs, project assembling tools;

Responsibilities:

•Participate in requirement, design, implementation, testing and support of custom banking solutions, which include features enhancements, new functionalities, and back-end systems integration.

•Define and manage resource plan together with the Project Manager aligning to the project schedule.

•Plan and drive the project's technical execution to achieve the committed scope and timeline.

•Monitor and report technical execution progress as well as all technical issues, risk or mitigation plan in a timely manner.

•Ability to coordinate multi-teams (e.g. customers, internal functional and technical SMEs), to understand business requirements, technical design and preparing of technical specifications.

•Assist in estimation of efforts and timescales for tasks delegated to the team.

•Contribute to design/code reviews for quality assurance and conformance to Company standards / guidelines.

•Hands-on participate in development and bugs fixing.

•Commit to continuous improvement and refinement of delivery.

•Strong technical knowledge and skills, consistently provide technical guidance and develop team members.

•Responsible for forward resource management, team building and staff career growth.

 

Requirements:

•Degree in Computer Sciences / Software Engineering / Information Technology.

•At least 5 years of working experience in Java EE development (preferably in the financial industry).

•Individual that is optimistic, proactive, good initiative, passionate, strives to achieve more as a team, and is able to motivate others.

•Understand design documentation standards such as Unified Modelling Language.

•Experience in various Java EE frameworks and design patterns. Preferably on Micro services architecture.

•Exposure in Java MVC frameworks such as Spring Boot.

Read more
Aakash Educational Services Limited
Omkar Pradhan
Posted by Omkar Pradhan
Remote, NCR (Delhi | Gurgaon | Noida)
4 - 8 yrs
₹8L - ₹12L / yr
Drupal
skill iconPHP
MySQL
skill iconHTML/CSS
skill iconAmazon Web Services (AWS)
+2 more
About Us

 

Aakash Educational Services Limited (AESL) is a leading educational institution in India that provides comprehensive test preparatory services for students preparing for medical and engineering entrance examinations, school/board exams and competitive and scholarship exams such as NTSE, KVPY, and Olympiads.  The “Aakash” brand is associated with quality test preparation and a proven student selection track record in various medical and engineering entrance examinations


What Would You Be Doing
  • Building and supporting backend and frontend development of websites and application projects
  • Producing appropriate and effective technical solutions
  • Working with a wider, distributed technology and project management teams to meet deadlines and maintain a high standard of code quality
  • Understanding, defining, and communicating functional and non-functional requirements
  • Working with our technical directors and project managers to define, scope, and estimate projects and features
  • Working with QA teams to address bugs and ensure our work output is of the best quality
What We Are Looking At
  • Excellent written and verbal English communication
  • Full exposure to both backend and frontend development on Drupal platforms
  • A strong and demonstrable background working with Drupal, especially 8/9
  • Experience building custom integrations, services, and modules within Drupal as well as integrating with APIs
  • Strong in Data Structure and Algorithm
  • Experience with Drupal templating using HTML5, CSS (SCSS is a bonus), and JavaScript and also the Twig templating engine
  • Competent with MySQL and optimising query and table performance within a Drupal platform
  • Working with cloud platforms like AWS
  • BE/B.Tech/MCA with 4+ years of experience in Drupal implementation
  • Strong experience in CI/CD processes (Jenkins, pipelines etc.)
  • Should have a good understanding of OOPs concept and Design Patterns like
  • Good Understanding of workflows
Read more
Fintech startup from UK who wants to set up in India
Fintech startup from UK who wants to set up in India
Agency job
via Multi Recruit by Santhosh Kumar KR
Remote, Bengaluru (Bangalore)
4 - 6 yrs
₹4L - ₹11L / yr
skill iconNodeJS (Node.js)
skill iconJava
skill iconAmazon Web Services (AWS)
skill iconAngularJS (1.x)
skill iconAngular (2+)
+1 more
  • Extensive experience in building REST APIs
  • Experience in building, managing, and enhancing backend / server-side development using java / java scripts. Expertise in NodeJS is preferred
  • The person must have built systems that consume and process volumes of data from various sources. Experience in handling and managing data in NoSQL databases such as Mongodb.
  • Extensive experience of building custom UI for web using the popular frameworks like angular and react. Experience in developing mobile UI is nice to have
  • Experience of working with code repositories such as Github and GitLab.
  • Fluent written and spoken English.
  • Experience of working on Cloud environments and experience in AWS is preferred.
  • Experience in Dockers and Kubernetes for deployments
Read more
Ry Rice
at Ry Rice
1 recruiter
Shashank Rajesh
Posted by Shashank Rajesh
Remote, Bengaluru (Bangalore)
2 - 4 yrs
₹3L - ₹4L / yr
skill iconLaravel
skill iconPHP
skill iconJavascript
Web Development
skill iconMongoDB
+11 more

Job description

 

Roles and responsibilities:

 

Platon is looking for a minimum 2 - 3 years experienced and motivated Full Stack professional with SaaS to be an integral part of Web Apps team. The team is an essential part of the Technology team at Platon and works on solving technical challenges related to processing, visualization and presentation of continually scaling data in an easily accessible manner on the Platon platform.

You should have hands on experience with PHP, Laravel, Java, COREJAVA, J2EE, javascript, Bootstrap, HTML, CSS, MYSQL/Oracle, MongoDB, Redis, AWS, Vuejs, Source code management (GitHub/Bitbucket),PWA etc. This role is ideal for you if you have a background in Full Stack development and are looking for the next level of career growth in a fast paced, learning based and merit driven work environment. mind Good to have experience in Native App development

 

 

What we are looking for:

  • Strong coding and design skills
  • Good command over Data Structures & Algorithms
  • The ability to produce bug-free and production grade code
  • Skills we consider PHP, Laravel, Java, COREJAVA, J2EE, javascript, Bootstrap, HTML, CSS, MYSQL/Oracle, MongoDB, Redis, AWS, Vuejs, Source code management (GitHub/Bitbucket),PWA.

 

The person will be responsible for:

  • To Develop Enterprise Applications using PHP, Laravel, Javascript, MySQL, PWA.
  • Help in Design of Web Application
  • Interaction with Clients
  • Quality & Timely Delivery
  • Helping Team Members on Technical issue

 

 

Required Candidate profile

  • Extensive experience in development using PHP, Laravel, Vue.js, MySQL and Javascript
  • Eye for Detail & Quality Delivery
  • Ability to work in a team environment
  • Must meet deadline
  • Knowledge of CRM/ERP
  • Mind Good to have experience in Android application development, COREJAVA, J2EE, React.js, js, PWA.

 

Read more
Techforceai
at Techforceai
5 recruiters
Surya Saipavan
Posted by Surya Saipavan
Hyderabad
3 - 7 yrs
₹12L - ₹15L / yr
Fullstack Developer
DevOps
Linux/Unix
Cloud Computing
RESTful APIs
+3 more
· Designer/Architect with 5-10 years of experience in Web UI & middleware REST API development · Well proven experience in JavaScript frameworks like NodeJS, JQuery, ReactJS · Knowledge on Node.js and frameworks such as Express JS , require JS etc. · Thorough understanding of React.js and its core principles · Familiar with newer specifications of EcmaScript and modern authentication mechanisms like JSON web tokens · Must have strong experience in Relational databases like MYSQL etc. and NoSQL databases like MongoDB, Cassandra etc. · Experience in cloud technologies like GCP, Azure is must · Should be able to work independently as well as lead the teams. · Knowledge on chatbot frameworks such as Microsoft Bot Framework · Experience in HTML5, CSS3, SASS, LESS is an added advantage
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.
ai_chip
Move faster with AI
We use AI to get you faster responses, recommendations and unmatched user experience.
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