A KDE developer works on KDE, an international free software community that develops open-source software. They design, develop, test, and maintain applications, widgets, and libraries for the KDE desktop environment. They collaborate with other developers, contribute to the KDE source code, fix bugs, and implement new features. They use programming languages such as C++, and tools like Qt and Git. They also engage with the KDE community, helping users and other developers, and participating in discussions to improve the KDE software. Additionally, they help in creating a user-friendly interface and ensure the software's compatibility with various operating systems.