Cutshort logo
Lister Technologies logo
Salesforce developer
Salesforce developer
Lister Technologies's logo

Salesforce developer

Nandakumar K's profile picture
Posted by Nandakumar K
2 - 5 yrs
₹6L - ₹12L / yr
Remote, Chennai
Skills
Salesforce
Salesforce Apex
Salesforce Lightning

Essential Skills :

  • Minimum 2 years of hands on experience in developing and delivering solutions on Salesforce Force.com platform including apex, triggers, Batch Apex, Visualforce and Integration with external systems
  • A self-starter with ability to work effectively with limited supervision
  • Ability to work with functional teams through all phases of the Software Development Lifecycle independent of the delivery methodology chosen
  • Strong in mapping business requirements to salesforce product features
  • Strong consulting skills to engage business for pipeline work
  • In depth knowledge on out of the box features, proposing solutions as per the business needs
  • Experience with Agile development practices will be a plus, •Experience in HTML, JavaScript, and CSS
  • Solid knowledge of SOQL.
  • Strong oral and written communication skills
  • Experience with jQuery will be a plus
  • Good grasping power to learn new things quickly and to understand the clients requirements
  • Multitasking abilities, solid technical (domain) skills, and excellent interpersonal ability
  • Strong analytical, problem solving, and troubleshooting skills
  • Knowledge of SOAP and REST APIs and JSON
  • Good knowledge of Salesforce recommended best practice around design and development
  • Ability to work independently and as part of a team
  • Aptitude for taking on technical challenges
  • com Certified Developer DEV401, Platform Developer I

 

Role Description :

  • Business requirement gathering, client interaction and be able to work in offshore / onshore model
  • Design, develop, test, document, and deploy high quality business solutions on the Force.com platform leveraging design patterns (standards solution specific)
  • Customize, develop and support solutions on salesforce.com, Force.com platform
  • Engage with the client and participate in process flow analysis and design
  • Communicate with other resources and with clients regarding status, technical issues and creative solutions
  • Demonstrate good judgment and pragmatic approach to deliver solutions on the Force.com platform that comply with the best practices
  • Provide the design and estimation for the requirement with defined process and quality
  • Review self and peers code/configuration as part of review process
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 Lister Technologies

Founded :
2000
Type :
Services
Size :
100-1000
Stage :
Profitable

About

Lister Technologies is a global technology company that offers Thought Leadership, Technology Expertise and Execution Excellence to deliver value to customers. It operates through two primary business divisions – Lister Digital and KPO. Lister provides expert Revenue Cycle Management services to mid-sized Healthcare providers in the USA and is one of the top Oracle Marketing Cloud partners worldwide. It is also amongst the earliest and most experienced Salesforce partners in South Asia. Lister works with some of the largest Fortune-500 clients across various industries.
Read more

Photos

Company featured pictures

Connect with the team

Profile picture
Shankar Natarajan
Profile picture
Shankar Natarajan
Profile picture
Vignesh Paramasivam
Profile picture
Jisha Balakrishnan
Profile picture
Nandakumar K
Profile picture
Govindarajan P
Profile picture
Ramya Selvan
Profile picture
Priya BSM

Company social profiles

bloglinkedintwitter

Similar jobs

Bolzano
Pritisha Zalpuri
Posted by Pritisha Zalpuri
overseas, Mauritius
8 - 12 yrs
₹25L - ₹30L / yr
Microsoft Dynamics
Microsoft Dynamics AX
Microsoft Dynamics NAV
Dynamics FO

Please note - this job is based physically out of Mauritius. You will have to physically relocate to Mauritius. Relocation support will be provided.


Max salary can go upto 30Lacs depending on current salary.


Tax structure in Mauritius is only 15%, so more in hand salary compared to India.


------------------------------------------------------------------------------


› Are you looking for a new challenge in a dynamic and fast-growing company?


Following our successes, we are expanding our capabilities and are looking for a Technical Architect on Dynamics 365 included Finance and Operations(formerly Dynamics AX).


› IN THIS ROLE

 In collaboration with the projects' solution architects, you will define the D365 technical architecture to be implemented.

 Your interpersonal skills will allow you to work in close collaboration with our clients' technical experts.

 Expert in Finance & Operations you have a good experience on one or two D365 Apps. You are willing to work on all available D365 Apps (Project Operations, CE, FS, ....), Dataverse...

 In collaboration with the team of functional consultants, you will participate in the enrichment and integration of the standard Microsoft Dynamics 365 solution to meet the challenges of our customers.

 You will translate our customers' functional specifications into technicalspecifications that can be used by the technical team, particularly to help our nearshore team.

 You are able to act as a technical leader and bring your experience to the whole team

 You can handle complex developments and interfaces

 You advise our customers on the use of Azure tools and D365 derivatives

 You provide support in the sales phase in the form of pre-sales activities and solution concepts, demonstrations, ....


OUR OFFER

 Work at one of the leading Swiss IT service providers, leader in Microsoft technologies with more than 100 collaborators in Dynamics 365

 A sector in strong development and a supportive culture with excellent opportunities for professional and personal training and development

 Interesting and varied tasks

 A close collaboration with Microsoft, as gold partner

 Work in local and international deployments 


ABOUT YOUR PROFILE


The ideal Candidate will have:

 A certification on Microsoft Dynamics AX2012R3 or Dynamics 365 FO for your functionalspecialty

 Master's degree or more

 8+ years’ experience in implementing Dynamics AX / Dynamics 365 in an IT service company (senior)

 Good process knowledge in development,support, ERP project orservices companies

 Very good knowledge of Dynamics AX/365 over the entire technical range, a second apps(D365CE, … ) is a plus.

 In-depth knowledge in a specialist area (e.g.ERP domain, Dataverse, CE, …) and corresponding expert knowledge in Dynamics AX/365

 Basic database knowledge and knowledge of the data structure of Dynamics AX/365

 Abilities to prepare architecture and analysis documents in a structured and understandable form

 Team player with conflict resolution potential

 Strong communication skills combined with social competence.

 French knowledge is a plus.

 Ability to travel to Switzerland for short term

Read more
vimo software development pvt ltd
Bengaluru (Bangalore)
3 - 6 yrs
₹6L - ₹15L / yr
skill iconAngularJS (1.x)
skill iconAngular (2+)
skill iconReact.js
skill iconNodeJS (Node.js)
skill iconMongoDB
+1 more

Your Responsibilities:

  • Responsible for overall tech stack of the product
  • Designing overall architecture of the web/ mobile application
  • Maintain quality and ensure responsiveness of applications
  • Exposure to security and data protection management
  • Building modular, reusable codes and libraries
  • Ability to build product from scratch & drive it to completion
  • Optimize applications for best user experience
  • Development experience for both mobile and web based products.
  • Unit Testing of developed modules

Skills:

Front-End

  • Web fundamentals like HTML, JavaScript, and CSS
  • CSS preprocessors like Sass, LESS, bootstrap
  • JavaScript frameworks like React js, AngularJS, or Ember etc.
  • Libraries like jQuery or Backbone.js
  • Front-end (CSS) frameworks like Foundation or Bootstrap
  • Web sockets

Back-End

  • Rest API design and development
  • CRUD (Create, Read, Update, Delete)
  • RESTful Services
  • Web fundamentals like React js, HTML, JavaScript, and CSS
  • Server-side languages like Javascript, PHP, Python
  • Database technologies like MySQL and MongoDB.
  • Web server technologies like Node.js, Nginx, ISS, etc.
Read more
EnterpriseMinds
at EnterpriseMinds
2 recruiters
Rani Galipalli
Posted by Rani Galipalli
Pune, Mumbai
5 - 8 yrs
₹1L - ₹16L / yr
Communication Skills
Business Analysis
Visio

Job Description:

  • 5-8 years of experience as business analyst preferably with some experience in healthcare domain
  • Experience in capturing/ defining requirements and creating business requirements document/ software requirements specifications
  • Extensive and hands on experience in creating wireframes using tools like Visio etc.
  • Experience in communicating with stakeholders across the board, including clients, business team, and the development team to make sure the goals are clear and the vision is aligned with business objectives
  • Experience as a BA in software development/ implementation projects is a must
  • Experience in creating and prioritizing the list of user stories/ backlog items and prioritize them based on the overall strategy and business objectives
  • Experience in overseeing the development of the product and taking necessary steps to keep the project on track
  • Strong communication skills, documentation skills. Excellent PPT, word and excel skills are a must

 Good to have

  • Have worked with hospitals or outpatient clinics or public sector healthcare entities
  • BA may have to travel for a few weeks Internationally

 

Read more
Credable
Credable
Agency job
via Getinz by Suganya Kannan
Noida, Mumbai, Chandigarh
15 - 20 yrs
₹10L - ₹15L / yr
skill iconJava
skill iconSpring Boot
Hibernate (Java)
Data Structures
Algorithms
+5 more
 • 15+ years of product development experience for large-scale secure systems with high volume and high-performance requirements.
      • Experience in the financial domain preferred.
      • Hands-on developer in Core Java with an excellent understanding of computer science fundamentals, data structures, algorithms and design patterns.
      • Experience with frameworks like Spring, Restful Webservices, Queuing systems, Angular, and Python is highly desired.
      • Deep understanding of several cloud providers such as AWS, Azure, Google etc.
      • Hands-on experience developing CI/CD pipelines for continuous development and integration.
      • Deep knowledge and experience of Java/J2EE and servers like Tomcat.
Read more
Initializ
Paras Arora
Posted by Paras Arora
Remote only
5 - 8 yrs
₹12L - ₹20L / yr
skill iconJava
J2EE
skill iconSpring Boot
Hibernate (Java)
skill iconAmazon Web Services (AWS)
Requirement
  • JAVA Microservices with AWS needed
  • Provide solution architecture & design involving Cloud and DevOps
  • Develop new microservices in a cloud-native way.
  • Ensure the unit testing and code coverage are achieved as per the agreed percentage.
  • Build reusable code and libraries for future use.
  • Optimize application for maximum performance and scalability.
  • Collaborate, and coordinate with team members and key stakeholders.
  • Communicate effectively with different stakeholders.
  • Ensure best practices & standards are followed during SDLC.
  • Takes ownership of the whole solution from a technical perspective and ensures adherence to defined Architecture & Design.
  • Ensures the latest technology standards, and guidelines are utilized for development.
  • Performs consistent & adequate code reviews & feedback to the team.
  • Training and induction of new resources on the projects.

 

Skills and Qualifications

  • Deep understanding of OOPs and OOAD.
  • Expert and hands-on in Java JEE and Spring framework, Spring Boot.
  • Should have experience with RESTful web services and API standards.
  • Should know various integration patterns in distributed environments.
  • Working knowledge of microservice architecture and different design patterns.
  • Hands-on in writing unit tests with Mockito and code coverage tools.
  • Hands-on data modeling (Logical physical).
  • Knowledge of RDBMS, SQL and any ORM framework (JPA, Hibernate etc.)
  • Should know Event-driven and asynchronous programming using message broker.
  • Should know about cloud IaaS, PaaS, SaaS and Serverless models of any cloud provider (AWS, Azure, GCP), preferably AWS.
  • Knowledge of JavaScript frameworks like NodeJS (For the Backend) and Angular React (For Frontend) will be added advantage.
  • Good to have DevOps related technologies like Container (Docker), Container Orchestrator (Kubernetes EKS)
  • Excellent in communication
Read more
Grooming Education Academy
at Grooming Education Academy
1 video
1 recruiter
atul D
Posted by atul D
Delhi
2 - 3 yrs
₹2.4L - ₹3L / yr
Communication Skills
Digital media
Social Media Marketing (SMM)
Digital Marketing
Assisting in the formulation of strategies to build a lasting digital connection with consumers. Planning and monitoring the ongoing company presence on social media. Launching optimized online advertisements to increase company and brand awareness.
Read more
Invendis Technologies India
at Invendis Technologies India
1 video
1 recruiter
Agency job
via PREMIER I NFORMATION by nirmala srinivasan
Bengaluru (Bangalore)
10 - 15 yrs
₹10L - ₹15L / yr
ASP.NET MVC

Ø Managing the customers independently. Prior experience in account management, creating, maintaining, and enhancing client relationships to yield business opportunities by working closely with clients CIO, CTO, PMO will be of advantage.

 

 

 

 

 

Ø  Managing internal Implementation team and resources.

 

 

 

 

 

Ø Implementation of standard product and creation of new modules.

 

 

 

 

 

Ø  Customer meeting to gather new requirements/ changes in existing requirements.

 

 

 

 

 

Ø  Understand market/ customer requirements the general need in various geographies.

 

 

 

 

 

Ø Customer Training-Full system training for existing customers.

 

 

 

 

 

Ø  Sound understanding of the practical application of agile development methods and leading software development teams in an Agile/Lean environment would be a great advantage.

 

 

 

 

 

Ø  Strong project management and technical fundamental skills to build complex enterprise software applications.

 

 

 

 

 

Ø Ability to leverage cutting-edge Agile and Lean practices to lead self-organizing teams to deliver software that does exactly what is needed as per client requirements.

 

 

 

 

 

Ø Ability to take the needs and challenges of clients and partner with them to formulate the delivery road map and project plans to support business strategies and goals.

 

 

 

 

 

Ø Deep understanding of Microsoft technologies, web development, architecture, configuration, deployment, and domain-driven designs.

 

 

 

 

 

Ø  Prior experience of Core Programming skills in Visual Studio, .Net Core, http://asp.net/">ASP.NET, C#, HTML5, CSS, jQuery, http://asp.net/">ASP.NET, MVC/ Angular JS, SQL Server, ORM (Entity Framework) is essential.

 

 

 

 

 

Ø Hands-on OOPS, Data Structure, and Test-Driven Development (TDD).

 

 

 

 

 

Ø Must have completed at least 2-3 SDLC projects in entity framework, MVC/ AngularJS & Web APIs.

 

 

 

 

 

Ø Hands-on with design Principles and Domain Driven Design.

 

 

 

 

 

Ø Must carry a Go-Getter attitude, enjoy working in a progressive and agile organization with greater self- driven ownership of project deliveries for multiple projects simultaneously.

 

 

 

 

 

Ø Experience in preparing technical Proposals, effort, and estimation.

 

 

 

 

 

Ø Should be passionate, hungry for continual learning to keep pace with the latest trends, technologies, and tools in Project Management.

 

 

 

 

 

Ø Knows all times, technical depth, and client expectations including the health of the project, critical path items, risks, and impact on timelines.

 

 

 

 

 

Ø Should be able to work on GUI + Libraries as well.

 

 

 

Ø  Change analysis for some of the new enhancements to be done in the system before integrating into the base system.

 

 

 

Ø  SRS for new enhancement

Read more
TensorIoT Software Services Private Limited, India
Aparna Nemani
Posted by Aparna Nemani
Remote only
2 - 6 yrs
₹6L - ₹15L / yr
skill iconJavascript
skill iconReact Native
skill iconReact.js
skill iconRedux/Flux
Deployment, automation, management, and maintenance of AWS cloud-based production system.
 Ensuring availability, performance, security, and scalability of AWS production systems.
 Management of creation, release, and configuration of production systems.
 Evaluation of new technology alternatives and vendor products.
 System troubleshooting and problem resolution across various application domains and platforms.
 Pre-production acceptance testing for quality assurance.
 Provision of critical system security by leveraging best practices and prolific cloud security solutions.
 Providing recommendations for architecture and process improvements.
 Definition and deployment of systems for metrics, logging, and monitoring on AWS platform.
 Designing, maintenance and management of tools for automation of different operational
 Train/mentor junior resources in AWS DevOps
 Document and maintain all platforms, CI/CD pipelines and other relevant integrations
 Research and improvise current implementations of DevOps platforms for continual improvement
Read more
Genesys
at Genesys
5 recruiters
Manojkumar Ganesh
Posted by Manojkumar Ganesh
Chennai, Hyderabad
4 - 10 yrs
₹10L - ₹40L / yr
ETL
Datawarehousing
Business Intelligence (BI)
Big Data
PySpark
+6 more

Join our team

 

We're looking for an experienced and passionate Data Engineer to join our team. Our vision is to empower Genesys to leverage data to drive better customer and business outcomes. Our batch and streaming solutions turn vast amounts of data into useful insights. If you’re interested in working with the latest big data technologies, using industry leading BI analytics and visualization tools, and bringing the power of data to our customers’ fingertips then this position is for you!

 

Our ideal candidate thrives in a fast-paced environment, enjoys the challenge of highly complex business contexts (that are typically being defined in real-time), and, above all, is a passionate about data and analytics.

 

 

What you'll get to do

 

  • Work in an agile development environment, constantly shipping and iterating.
  • Develop high quality batch and streaming big data pipelines.
  • Interface with our Data Consumers, gathering requirements, and delivering complete data solutions.
  • Own the design, development, and maintenance of datasets that drive key business decisions.
  • Support, monitor and maintain the data models
  • Adopt and define the standards and best practices in data engineering including data integrity, performance optimization, validation, reliability, and documentation.
  • Keep up-to-date with advances in big data technologies and run pilots to design the data architecture to scale with the increased data volume using cloud services.
  • Triage many possible courses of action in a high-ambiguity environment, making use of both quantitative analysis and business judgment.

 

Your experience should include

 

  • Bachelor’s degree in CS or related technical field.
  • 5+ years of experience in data modelling, data development, and data warehousing.
  • Experience working with Big Data technologies (Hadoop, Hive, Spark, Kafka, Kinesis).
  • Experience with large scale data processing systems for both batch and streaming technologies (Hadoop, Spark, Kinesis, Flink).
  • Experience in programming using Python, Java or Scala.
  • Experience with data orchestration tools (Airflow, Oozie, Step Functions).
  • Solid understanding of database technologies including NoSQL and SQL.
  • Strong in SQL queries (experience with Snowflake Cloud Datawarehouse is a plus)
  • Work experience in Talend is a plus
  • Track record of delivering reliable data pipelines with solid test infrastructure, CICD, data quality checks, monitoring, and alerting.
  • Strong organizational and multitasking skills with ability to balance competing priorities.
  • Excellent communication (verbal and written) and interpersonal skills and an ability to effectively communicate with both business and technical teams.
  • An ability to work in a fast-paced environment where continuous innovation is occurring, and ambiguity is the norm.

 

Good to have

  • Experience with AWS big data technologies - S3, EMR, Kinesis, Redshift, Glue
Read more
Testing Ground
at Testing Ground
2 recruiters
Bryan Long
Posted by Bryan Long
Remote only
0 - 1 yrs
$4.0K - $4.4K / yr
Graphic Designing
Graphic
User Experience (UX) Design
skill iconHTML/CSS
User Interface (UI) Design

The Company


Testing Ground is disrupting the way new business ventures develop and grow in the different industries. We help founders and innovation leads in companies figure out where their new business vertical, test demand for it from customers across Asia and help them scale it up. We hand the new to the world and new to market products and solutions which will change the way the industry operates. We also work towards creating a workforce who is able to help other companies test and grow their business model.  

Testing Ground is a Singapore based startup with early satellite bases in Indonesia, Malaysia, India, Bangladesh, China and Vietnam. Joining us means that you will get the opportunity to learn from the founding members. Our founder has deep experience building and mentoring start-ups across Southeast Asia. His previous startup counts Eduardo Saverin, Co-founder of Facebook, as one of their investors. Our co-founders are experts in community and partnership development in China and Singapore as well as skilled in future oriented capabilities such as digital marketing, viral growth, content marketing and latest innovation strategies.

At Testing Ground, we want our team to be made up of people who have the ability to become the best. We practice Lean Startup and Agile. We do stand-ups and run experiments often. We have an open work culture but yet we are very focused and very energetic.

If you would like to learn and get your hands dirty in doing the work related to the latest innovation and methodology to creating a sustainable business model, this is the place for you. 

As a startup, everyone in the team are do-ers and want to make a name for themselves. We are driven and open to new ideas. Join us and have a chance to craft out your own growth as well as the company’s growth. 

 

The Opportunity


Unleash your capability with us

Small and medium enterprises (SMEs) are facing an upcoming upheaval with technology disrupting the way things are currently run. Beyond providing consulting services to these companies, we want to help them by providing them with a clear methodology to support them through this transition. 

That is where you come in.

 

As a graphic designer at Testing Ground, you will have the opportunity to conceptualise ideas and craft inspiring designs, as well as to play a part in envisioning the creative direction for these companies. We are looking for someone who is always hungry to learn new tools and skills to develop thoughtful, creative illustrations that communicate key messages in a clean, simple way. Apply now if you thrive on exploring new concepts and enjoy watching your ideas come to life – from conceptualisation to production.

 

This is a full-time role (9am-6pm, Mondays to Fridays), with a monthly salary of 363 USD.


Competencies created: You will be able to

  • Develop design concepts for business objectives and goals
  • You'll learn how to deliver value to projects through objective-based design such as developing the style and vision for the clients that we work with.
  • You’ll get to design for business success for creative and effective delivery of branding services
  • Manage various stakeholders and project requirements
  • You’ll have the opportunity to work with our team to ensure collaterals are delivered on time
  • You’ll manage multiple projects with concurrent deadlines, ensuring high quality and accuracy of final deliverables through proofreading

 

About the Role:

  • Create Visual Brand Identity
  • Conceptualise a creative direction for Testing Ground’s projects
  • Conceptualise and design branding/marketing materials for both print and web related marketing material
  • Produce new artwork based on brand guidelines agreed with our team
  • Create print and digital advertising materials



  • Develop Key Visuals and Collaterals for Marketing Campaigns and Events
  • Assist in the management of website, newsletters and all other company materials, where necessary
  • Design all graphic, sales and marketing materials e.g. EDM / Posters / Banners
  • Work with us in crafting visually compelling presentations



  • Manage Design from Concept to Production
  • Work according to briefs for the branding needs and guidelines
  • Ensure design specifications are production-ready
  • Engage with external printers or contractors/suppliers/vendors to ensure the highest quality of materials and that deadlines are met
  • Proper documentation of all design files

 

 

 

Why You Will Love Working with Testing Ground:

  • If you have been thinking of starting your own business, this position will give you an in-depth insight to what works and doesn’t in the different industries and countries across Asia.   
  • The firm believes that it is critical to encourage personal development to have a successful team. As such, we have a variety of online learning courses which you can use to pick up different skills and capabilities. 
  • You will be exposed to different platforms and tools to help you become more efficient in doing your job.

 

Experience:

 

At least Diploma in Art/Design/Creative fields 

 

Skills Required:

  • Familiarity with Adobe Creative Suite especially Illustrator and Photoshop
  • Familiarity in Adobe InDesign for desktop publishing
  • Ability to convey company’s message in line with brand’s guidelines through original design
  • Ability to create strong design concepts
  • (good to have) Skilled in video editing
  • (good to have) Skilled in photography and videography
  • (good to have) Knowledge of photo editing in Adobe Photoshop or Lightroom

 

What we’re looking for in you:

  • Desire to learn and adapt to new technologies
  • Able to work independently and proactively in a team
  • Strong communication skills to liaise with marketing team and external vendors
  • Ability to prioritize and manage multiple projects deadlines
  • Positive attitude and willingness to learn
  • Keen eye for detail

 

P.S: Assess us like we assess you. If you’d like to check out who our founder is, you can connect with him via his LinkedIn page url here and say “Hi, I saw your job post on….” :https://www.linkedin.com/in/thehappybryan/"> https://www.linkedin.com/in/thehappybryan/

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