We hang out on irc.freenode.net in the #mana channel and we're using a mailing list to communicate outside of IRC (though mailing list membership has to be manually approved so that we don't have to face spam).
We are using a sub forum of The Mana World forums: http://forums.themanaworld.org/viewforum.php?f=31
Task and bug tracker
We're using Mantis, at http://bugs.manasource.org/.
Available at http://github.com/mana.
Running at http://testing.manasource.org on port 9601