An application developer is responsible for designing, developing, and maintaining software applications for various platforms such as desktop, mobile, or web. They collaborate with stakeholders, including clients, users, and other members of the development team, to understand requirements and translate them into functional and user-friendly applications. Application developers use programming languages, frameworks, and development tools to create applications that meet performance, security, and usability standards. They also conduct testing, debugging, and troubleshooting to ensure the quality and reliability of the applications.