SourceForge used to be free software. GForge (e.g: GNU Savannah) is based on that. Berlios.de
is based on an older version of that, but IIRC they don't publish its source with the various
adjustments they made there.
As for distributed bug-tracking system: I'm not sure this can actually work well. How do you
merge the comment I have added to the bug and the comment you have added to the bug? And if I
also closed that bug?