SOURCE CODE
The source code of the OpenMS library as well as the TOPP tools and TOPPView are hosted on GitHub. The most important repository for starting developers is OpenMS itself. Its third-party dependencies are built with vcpkg, which the CMake presets in the repository set up; see Building OpenMS. The source code is released under a three-clause BSD license.
DOCUMENTATION
A good starting point for developers is the OpenMS GitHub wiki. For a quick dive into developing your own, see the Developer FAQ and the Adding your own tool to the TOPP suite.