The development version of Diffuse is mainly meant for developers and may be unstable. The development code resides in a Subversion repository. Use this command to get a local copy of the code:
$ svn co https://diffuse.svn.sourceforge.net/svnroot/diffuse/trunk diffuse
The Subversion repository may also be browsed using the web interface.
If you are interested in coding, you can take a look at existing bug reports and feature requests for ideas or just code what you like and bring it up for discussion on the mailing list or bug tracker. If you are interested in translating the user interface or documentation, please read the "README" file in the "translations" directory.