Cutshort logo
urbansoft™ logo
Opencart/PHP Developer
Opencart/PHP Developer
urbansoft™'s logo

Opencart/PHP Developer

saravanan aa's profile picture
Posted by saravanan aa
2 - 3 yrs
₹3.6L - ₹5L / yr
Remote only
Skills
skill iconVue.js
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconReact.js
skill iconJavascript
skill iconPHP
MySQL
skill iconLaravel
skill iconCodeIgniter
OpenCart
skill iconHTML/CSS
API
Payment gateways

We are seeking a highly skilled Opencart Developer to join our dynamic team. The successful candidate will be responsible for designing, developing, and maintaining high-quality e-commerce websites using the Opencart platform. As an Opencart Developer, you will work closely with our team of designers, developers, and project managers to ensure that all projects are completed on time and to the highest quality.

Key Responsibilities:

  • Develop and maintain Opencart website
  • Customization
  • Design and implement custom Opencart themes
  • Develop custom Opencart modules and extensions
  • API Integration
  • Payment Gateway Integration
  • Troubleshoot and debug Opencart websites
  • Optimize website performance and speed
  • Collaborate with the team to ensure website functionality and user experience
  • Stay up-to-date with the latest Opencart and PHP development trends and technologies
  • Testing Knowledge
  • Maintaining Hosting & Server

Qualifications:

  • A minimum of 1-year experience in developing Opencart websites using PHP
  • Strong proficiency in PHP, MySQL, HTML, CSS, and JavaScript
  • Experience in developing custom Opencart themes and modules
  • Experience in troubleshooting and debugging Opencart websites
  • Strong problem-solving and analytical skills
  • Excellent attention to detail and ability to deliver projects on time
  • Good communication and interpersonal skills

Education:

  • A degree in Computer Science, Information Technology or a related field is preferred but not mandatory.


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 urbansoft™

Founded :
2008
Type :
Products & Services
Size :
20-100
Stage :
Profitable

About

Urbansoft, a leading digital transformation company established in 2014, offering innovative solutions to businesses worldwide. With an unwavering commitment to excellence, we've become a trusted partner for organizations seeking to thrive in the digital era. With an impressive portfolio of satisfied customers across multiple countries, we have established ourselves as a trusted partner in driving digital growth and success.
Read more

Company social profiles

linkedin

Similar jobs

Company automate the API workflow for developers.
Company automate the API workflow for developers.
Agency job
via Qrata by Rayal Rajan
Bengaluru (Bangalore)
0 - 2 yrs
₹6L - ₹8L / yr
skill iconJava
skill iconJavascript
skill iconReact.js
skill iconAngular (2+)
skill iconAngularJS (1.x)
+7 more

As a Junior Full Stack Developer, you will have the opportunity to work with a dynamic team and contribute to the development of our cutting-edge products. This is an excellent opportunity for motivated individual to enhance their skills and gain valuable experience in Java and React.js development.


Responsibilities:


1. Full Stack Development: Collaborate with senior developers and project teams to design, develop, and maintain web applications using Java and React.js.

2. Front-End Development: Implement user interfaces and create interactive web pages using HTML, CSS, and JavaScript frameworks like React.js.

3. Back-End Development: Design and develop server-side logic using Java, including building RESTful APIs, integrating with databases, and implementing business logic.

4. Database Management: Work with databases (e.g., MySQL, PostgreSQL) to design schemas, write queries, and optimize database performance.

5. Bug Fixing and Troubleshooting: Identify and resolve technical issues and bugs, ensuring the stability and functionality of the web applications.

6. Code Reviews: Participate in code reviews to maintain code quality, identify potential improvements, and ensure adherence to best practices and coding standards.

7. Learning and Growth: Stay updated with the latest industry trends, tools, and technologies, and continuously enhance your skills as a Full Stack Developer.


Qualifications:

1. Education: Bachelor's degree in Computer Science, Software Engineering, or a related field. Relevant work experience and projects will be considered.

2. Programming Skills:

● Strong knowledge of Java programming language and its core concepts.

● Familiarity with front-end development using React.js or similar JavaScript frameworks.

● Experience with HTML, CSS, and JavaScript.

3. Database Knowledge: Understanding of database concepts and experience working with SQL databases.

4. Web Technologies: Understanding of web development principles, RESTful APIs, and HTTP protocols.

5. Problem-Solving: Strong problem-solving skills and the ability to analyze and debug issues effectively.

6. Team Player: Demonstrated ability to work collaboratively in a team environment, share ideas, and contribute to the overall success of the project.

7. Self-Motivated: Proactive and eager to learn new technologies and tools independently.

8. Communication: Effective verbal and written communication skills to collaborate with team members and stakeholders.

9. Attention to Detail: Meticulous attention to detail and the ability to write clean, efficient, and maintainable code.

10. Enthusiasm: Passion for software development and a drive to build high-quality applications.

Read more
Bengaluru (Bangalore)
2 - 4 yrs
₹3L - ₹4L / yr
skill iconVue.js
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconReact.js
skill iconJavascript
+5 more

Dear PHP Laravel Engineer,


Greetings from Gerizim Technologies Pvt. Ltd., Bangalore!


We are excited to announce an incredible opportunity for experienced PHP Laravel Engineers to join our SaaS startup. With a minimum experience requirement of 2-3 years in PHP with Laravel framework and its supporting tools, we believe that your expertise and skills will greatly contribute to our innovative projects.


At Gerizim Technologies, we are building a revolutionary SaaS platform that has the potential to reshape the industry. As part of our core team, you will have the chance to collaborate with senior-level individuals and work on cutting-edge projects that push boundaries and drive technological advancements.


While we understand that our salary package may not be as competitive as some larger companies, we offer a unique proposition for those who are willing to embark on a rewarding journey with us. We are seeking candidates who are committed to supporting our startup for a period of 2 years. In return, you will have the opportunity for career growth, promotion, and a significant increase in salary and benefits after this initial period.


As an integral member of our team, you will be involved in developing innovative solutions using PHP Laravel, along with supporting technologies such as jQuery, JavaScript, CSS, HTML, and databases like PostgreSQL and MySQL. You will have the chance to work alongside talented professionals, learn new technologies, and contribute to the success of our SaaS platform.


We understand that you may have other options available to you, but we believe that joining our startup will provide you with a unique opportunity for professional and personal growth. We value the willingness to learn, adapt, and face challenges head-on, and we are committed to supporting your development throughout your journey with us.


If you are ready to embrace new technologies, be part of a dynamic startup culture, and work on groundbreaking projects, we invite you to join our team. Your contributions will directly impact our success and shape the future of the industry.


If you have any further questions or would like to discuss the position in more detail, please do not hesitate to reach out. We look forward to welcoming you to our team and embarking on this exciting journey together.

Read more
StarkFlow LLC
at StarkFlow LLC
1 recruiter
Sonam Mishra
Posted by Sonam Mishra
Remote only
3 - 8 yrs
₹7L - ₹9L / yr
skill icon.NET
ASP.NET
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconJavascript
+7 more

Hi,

Greetings from Starkflow!!

 

We are hiring for a Senior Full Stack Developer for our direct client for a Full Time/Permanent role opportunity.

 

About Client: The Client is an AI SaaS and Cloud Based company, doing Computer Vision and Machine Learning based in Tel Aviv, creating high-end technologies for autonomous systems. They work in several different areas, but their focus is on Asset Inspection development.


Title: Senior Full Stack Developer

Location: Delhi or Bangalore (Remote)

Job Type: Full time

Experience: 2-5+ years

Key Skill-set: MVC 5, .Net Core, C#, MySQL, CSS, HTML, JavaScript - is a must with extensive knowledge of JavaScript, jQuery, HTML, CSS, AJAX, and JSON.

Job Description:

 

Full Stack Developer Responsibilities:

•       Developing front-end website architecture.

•       Designing user interactions on web pages.

•       Developing back-end website applications.

•       Creating servers and databases for functionality.

•       Ensuring cross-platform optimization for mobile phones.

•       Ensuring responsiveness of applications.

•       Working alongside graphic designers for web design features.

•       Seeing through a project from conception to finished product.

•       Designing and developing APIs.

•       Meeting both technical and consumer needs.

•       Staying abreast of developments in web applications and programming languages.


Full Stack Developer Requirements:

•       Degree in computer science.

•       Must have HTML / HTML 5 and CSS work experience

•       Good working knowledge of Bootstrap

•       Knowledge of MVC Patterns & other design patterns.

•       Will be responsible for designing, coding, and modifying websites, from layout to function.

•       Strive to create visually appealing sites that feature user-friendly design and clear navigation.

•       Hands-on experience with Web Applications and programming languages such as HTML, CSS, JavaScript, jQuery, C#, and API.

•       On-time delivery of projects and team coordination is mandatory.

•       Familiarity with databases (e.g. MySQL)

Read more
FOXTROT SOLUTIONS LLP
Gurugram, Delhi, Noida, Ghaziabad, Faridabad
2 - 3 yrs
₹2L - ₹3L / yr
skill iconPHP
skill iconJavascript
skill iconReact.js
skill iconAngular (2+)
skill iconAngularJS (1.x)
+5 more

Job description

Looking for a skilled word press developer responsible for both front-end and back-end development including the implementation of WordPress themes and plugins as well as site integration and security update.

In this role you will:

• Design and build the website's front end.

• Create the website architecture.

• Generate WordPress themes and plugins.

• Trouble shoot content issue.

We are looking for someone who has:

• Bachelor’s degree or equivalent experience in web designs.

• Experience of minimum 1 year in WordPress

• Knowledge of front-end technologies including CSS, HTML, java script, and jQuery.

• Must have good knowledge of PHP, and MySQL also.

SALARY: Up to 3.6LPA


Job Type: Full-time

Salary: ₹15,000.00 - ₹30,000.00 per month

Benefits:

• Flexible schedule

• Health insurance

• Paid sick time

• Paid time off

• Provident Fund

Schedule:

• Day shift

Supplemental pay types:

• Commission pay

• Overtime pay

• Performance bonus

Ability to commute/relocate:

• Gurgaon, Haryana: Reliably commute or planning to relocate before starting work (Required)

Education:

• Bachelor's (Preferred)

Experience:

• total work: 1 year (Required)

• WordPress: 1 year (Required)



Read more
Xure Software Solutions LLP
Praveen Kumar
Posted by Praveen Kumar
Gurugram
1 - 3 yrs
₹10L - ₹12L / yr
skill iconNodeJS (Node.js)
skill iconReact.js
skill iconAngular (2+)
skill iconAngularJS (1.x)
skill iconExpress
+2 more

About the job

We are looking for an experienced individual who can work with us. The selected developer would help us in developing new backend services, update / change older working services, creating REST APIs for frontend, and maintain existing code and integration to other Providers with High Quality and re-usable code. Further it will be expected out of the developer to help in optimizing components for maximum performance across a vast array of edge cases, and test the code.


Particulars of the job


REQUIREMENTS

  • Must be passionate about learning new technologies.
  • 2+ years of experience in developing web based applications.
  • Must have experiencing in node.js / postgresql.
  • Ability to solve architecture level problems.
  • Experience in leading the team, have lead the team of junior developers in past.

 

What we appreciate?

A perfect candidate should hold or think the following things are important.

Values - Orderliness • Transparency • Merit • Productivity • Smart work

Abilities - Pro-activeness • Problem solving aptitude • Responsive • Quick learner • Leadership traits

Skills - • NodeJS • JavaScript • Typescript • RESTful APIs • HTML / CSS • PostgreSQL • SQL Server • Networking • Templating engine • Git

Brownie points - Good communicator • Organized • Awareness of new approaches/practices in domain • Awareness of online communities

Who are we?

We are a SaS startup, who is building software for other start-ups, and helping others on the way stand. Our mission is to reduce the barriers to launching a tech startup.

Xuresolutions.in 


Why work with us?

  • We promote an open culture based on trust and ownership.
  • We like to work in an idea meritocracy. Ideas and believability of individuals over seniority/title.
  • Our working schedule revolves around Monday to Friday.
  • Working hours are 10 AM to 7 PM officially. However, we aim for maximum overlap and coordination rather than pointless strict conformity (we aren’t a school!)
  • We work a flexible week depending on the current team’s performance and needs. Roles and Responsibilities
Read more
Vavia Technologies Pvt. Ltd.
Alan DSouza
Posted by Alan DSouza
Remote, Bengaluru (Bangalore)
6 - 11 yrs
₹15L - ₹24L / yr
skill iconRuby on Rails (ROR)
skill iconJavascript
MySQL
skill iconAmazon Web Services (AWS)
skill iconAngular (2+)
+1 more
We are a fast paced startup that has both inhouse products and provides technology consulting to other product companies as well. Given this, you will have deep exposure to a several innovative products.

However, Most importantly, you will need to be very passionate about building products and will need to thrive in a startup environment. 

Responsibilities - 
  • Architect, develop and maintain core products and services of the company.
  • Create database architecture and best practises for optimization in speed and product operating costs.
  • Design client-side and server-side architecture
  • Build the front-end of applications through appealing visual design
  • Develop and manage well-functioning databases and applications
  • Write effective APIs with high-volume large scale transaction processing capabilities.
  • Collaborate with design teams to ensure flawless UI and UX is achieved 
  • Build features and applications with a mobile responsive design
  • Write technical documentation
  • Test software to ensure responsiveness and efficiency
  • Work with customers in evaluating technical requirements.
  • Work closely with the product managers to achieve product vision and goals
  • Review work of other developers and contractors, provide feedback and mentoring.
  • Assist in the hiring of technical talent.

Requirements & Qualifications
  • Proven experience as a Full Stack Developer or similar role for atleast 3 years 
  • In depth knowledge of Ruby on Rails, NodeJS, ExpressJS or Restify
  • Experience implementing applications using Angular 1 or React
  • Experience creating front end applications using HTML5, Angular, LESS/SASS
  • Hands on experience with JavaScript Development on both client and server-side
  • Automating the building and deploying of code along with continuous integration (Jenkins/Hudson) and version control (SVN, Git)
  • Strong experience is deploying and managing application in AWS and Google Cloud
  • Creating secure RESTful-based web services in XML and JSON, Javascript, JQuery
  • Experience with modern frameworks and design patterns, minimum 2 years experience with MEAN Fullstack paradigm

Most important requirements and TLDR - 
  • Know how to create apis and applications
  • Know how to architect and scale databases
  • Know how to build front end for applications
  • Know how to deploy applications on the cloud
Read more
Lowest brokerage fee in Stock market Industry. (AB1)
Lowest brokerage fee in Stock market Industry. (AB1)
Agency job
via Multi Recruit by Ravish E
Bengaluru (Bangalore)
2 - 3 yrs
₹4L - ₹6L / yr
skill iconReact.js
skill iconGit
skill iconHTML/CSS
skill iconJavascript
Angular
+1 more
  • Must have knowledge in Angular or React frontend and Node JS
  • Write reusable, testable, efficient code
  • Knowledge of creating front-end applications using HTML5, CSS, and Javascript.
  • Candidates should have Knowledge of recent Angular versions and should be comfortable working independently.
  • Should have working experience with database modeling, ability to plan DB schema and write queries with ease(MongoDB, MYSQL, Redis)
  • Implementation of security and data protection
  • Comfortable working with Git/Github
  • Ability and willingness to manage multiple projects and tasks.
Read more
Distributed Energy
at Distributed Energy
2 recruiters
Ruchir Punjabi
Posted by Ruchir Punjabi
Remote, Kochi (Cochin), Chennai
2 - 5 yrs
₹4L - ₹10L / yr
Wordpress
skill iconHTML/CSS
Fullstack Developer
skill iconPHP
MySQL
+3 more

The ideal candidate is a self-motivated, multi-tasker, and demonstrated team-player. You will be a lead developer responsible for the development and management of two of our customer facing websites. You should excel in working with scaling applications and frameworks.

 

The core skillset required is:

* Wordpress (inbuilt functions, theme and architecture level understanding)

* PHP

* MySQL

* HTML5 / CSS3

* Javascript (and related frameworks/libraries)

* Git

* RESTful APIs

 

Responsibilities

  • Translating designs and functionality into code
  • Maintaining dev and live versions of websites
  • Writing clean, high-quality, high-performance, maintainable code
  • Develop and support software including applications, database integration, interfaces, and new functionality enhancements
  • Coordinate cross-functionally with external and internal teams
  • Support test and deployment of new products and features
  • Participate in code reviews

 

Qualifications

  • Bachelor's degree in Computer Science (or related field)
  • 2+ years of relevant work experience
  • Expertise in Object Oriented Design, Database Design, and XML Schema
  • Ability to multi-task, organize, and prioritize work

 

Mentorship and Support

* You will work directly with the Co-Founder of the business who will provide direct mentorship both around development as well as (if interested) help you cultivate business-side skills

Read more
A leading Media Data and Analytics Firm
A leading Media Data and Analytics Firm
Agency job
via WWWNEXTLEAPADVISORYCOM by Divya Sethi
NCR (Delhi | Gurgaon | Noida), Pune, Bengaluru (Bangalore), Hyderabad, Chennai
7 - 9 yrs
₹10L - ₹21L / yr
skill icon.NET
ASP.NET MVC
skill iconC#
skill iconMongoDB
skill iconJavascript
+4 more
YOUR RESPONSIBILITIES
• Development and unit testing of web application including front-end (SPA) and back-end (microservices),
maintenance & support of the same
• Provide assistance to Project Managers and Technical Leads in the planning of projects (eg provision of
estimates, risk analysis, requirements analysis, technical options)
• Software Design
• Involvement in full life cycle of projects (including requirement analysis and system design, development
and support if required)
• Support and work collaboratively with teams across areas of design, development, quality assurance and
operations
• Commit your knowledge and experience into team success
• Be prepared to travel (when needed) to work with other offices
• Attend meetings if required to discuss and demonstrate solutions at both technical and business level
• To be a single person responsible for overall technical health and Tech Ownership
• To be a knowledge keeper for product, its architecture, design and implementation details
• Provide overall mentorship, coaching and on-demand trainings to improve and unify development style
REQUIRED SKILLS AND EXPERIENCE
• 7+ years in application development
• Understanding the sense of OOP/OOD/DDD
• Using of OOP and patterns
• ASP.NET MVC experience
• Database experience (MS SQL, MongoDB, ElasticSearch or similar) and ORM technologies (LINQ, EF or similar)
• MSBuild
• Performance optimization
• Security design and implementation
• API design and development including RPC-like / REST
• Distributed message based application design and implementation
• TDD practices
• CI/CD practices
• HTML5/CSS3/JavaScript/TypeScript and AJAX experience
• SPA (Single Page Application) design and implementation (Angular, React, Vue.js or similar)

DESIRABLE SKILLS AND EXPERIENCE
• CQRS and Event Sourcing pattern Experience
• AWS-based development
• Serverless
• Docker
• .Net Core
• MongoDB
• ElasticSearch
• Knockout.js
• Vue.js
• Design and usability skills are a plus
• Multi-tenant application development experience is a huge plus

PERSONAL SKILLS
• Clever personality
• Strong spirit skills set: conflict resistant, self -motivated, result-oriented, responsible, honest, “open”,
courageous
Read more
This position is for Product Base Company
This position is for Product Base Company
Agency job
via Heron Strategic Consulting Pvt. Ltd. by Samarpana Rao Manne
Hyderabad
3 - 7 yrs
₹8L - ₹15L / yr
skill iconJavascript
ASP.NET
SQL server
ASP.NET MVC
skill iconGit
+3 more

Dear Applicant,

Greetings from Heron!

We are pleased to introduce ourselves as a company initiated to bridge the gap between companies, organizations and resources. 

 

We are ‘Heron Strategic Consulting Pvt. Ltd.’- a professional consulting organization which provides solutions to transform Human Resources more employable and solve the major problems faced by companies in managing their finances. We identify the problems faced by emerging startups in finance and HR domain, and we are trying to solve it by tech enabled platform (under construction)

As discussed, We have an open position for Software Fullstack Developer  - Asp.net with our Client in Hyderabad. We found your profile matches with our requirement, we want to check if you would be interested in applying for this position. Below is the job description for your reference.
 
 If you have questions please feel free to contact us. Kindly share your updated resume.
        

 

 

Job Role

Developer/Senior Developer – Full Stack (ASP .Net, C#, SQL Server) 

Experience Level: 2-7 Years. 


Skills required: 

• Strong knowledge on http://asp.net/" target="_blank">ASP.NET web technologies.

• Proficient in C#, Web API, MS SQL Server, Java Script, CSS, HTML and Jquery 

• Strong understanding of Object Oriented Programming. 

• Experience in design, develop and test individual modules using Agile Methodology. 

• Good understanding of design principles for building a scalable application. 

• Proficient in developing optimized and responsive UI.

• Hands-on experience with Web API and Service Oriented Architecture. 


• Excellent Communication, presentation, problem-solving and team working skills. 

• Added advantage for candidates recognized in Coding Contexts or Hackathons. 

• Candidates with any certifications, awards or work recognition from previous organization are given preference. 

Job Overview

We are seeking a passionate ASP. Net Developer to join our EffiaSoft Team at Hyderabad Location. In this role, you will work with our team of talented engineers to design and build the next generation web applications. Candidates must possess high coding practices through good design, documentation, unit testing along with excellent problem solving and strategy methods. Also, should get updated with the latest technologies and must have good decision making and communication skills.

 

 

Roles & Responsibilities

• Design, build and maintain efficient web based services and applications using .Net programming languages such as ASP. Net, C# Web API and MS SQL Server.

 • Collaborate with internal teams to produce software design and architecture. 

• Integrate data storage solutions by developing SQL Server databases which include queries, triggers and stored procedures. • Ensure the best possible performance and quality by working closely with the quality assurance team to ensure delivery of high quality and reliable web applications. 

• Troubleshooting, debugging and unit-testing code for robustness, including edge cases, usability, and general reliability along with technical designs. 

• Interact with the clients to define project features and requirements and make necessary changes and update to the applications as per the requirement. 

• Testing the application on different web browsers to ensure a standard user experience for the clients across all platforms.

 • Continuous identification, evaluation and implementation of new technologies to improve development efficiency. 

Qualification

BE, B tech, ME M tech, BS or MS degree in Computer Science Engineering

 

 

Notice Period

 
 
Please share me your latest resume at the earliest.
 
What are the technologies are you working: .
What is your experience in each technologies
Asp.Net: 
C#: 
Web Api: 
Javascript: 
jquery: 
http://vb.net/" target="_blank">vb.net: 
OOPs Concept experience
Agile Methodology Exp?
crystal report: 
Database: 
Troubleshooting:
GIT Tools: 
UI Responsive
Which project you currently working? 
What is duration of the project?  
What is strength of the project: 
What is you role and responsibility in the current project?
what is your career goal?
what are you strengths and weakness?
Do you have experience in Angularjs:
 
please feel free to fill below details :
 
Full Name:
Years of Exp:
Relevant Years of exp:
Current Organisation:
Current Designation :
current CTC:
Expected CTC:
Qualification:
Skills:
Notice Period:
Reason for change?
current location :
Willing to relocate to Hyderabad and why?
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