You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/eclipse/smarthome - Project repository hosted on GitHub.
https://github.com/eclipse/smarthome.osgi-ri.enocean - Project repository hosted on GitHub.
https://github.com/eclipse/smarthome-packaging-sample - Project repository hosted on GitHub.
https://github.com/eclipse/smarthome-designer - Project repository hosted on GitHub.