SOURCE CODE The source code of the OpenMS library as well as the TOPP tools and TOPPView are hosted on GitHub. The most important repositories for starting developers will be OpenMS itself and its contrib (i.e. its dependencies). 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.