With actual version of the files (r4), you can already have a jabber server (ejabberd) with an account for each GForge user.

In addition, each developer can see some groups in his buddy list, named after the projects he works on, in which he can found other developers' JabberID.

For instance, if bob and alice are developers in the project named 'Example' , they will both see in their buddy list a group named 'Example project'.
In this group, bob will see alice, and... (see more)