While the sourcecode is currently hosted on [gitlab](https://gitlab.com/GrafX2/grafX2/), the bugtracker and developer docs are hosted on [Trac](http://pulkomandy.tk/projects/GrafX2). Drive your browser there for a lot of useful information on GrafX2 development, internals, and roadmap. You can also join the #grafx2 channel on Freenode for more direct interaction with other developers.