Ye' old general discussion board. Basically, for everything that isn't covered elsewhere. Come here to shoot the breeze, shoot your mouth off, or whatever suits your fancy. This forum is not for asking programming related questions.
And I find its integration with Project Server very handy, and I'm not aware of any such OSS platform (email+pim+task management). When Zimbra will be available as a FreeBSD port, I'll definitely try it, but until then...