I've been using Community Server, but that's because I'm a MS web programmer (it runs on .NET and thus needs IIS server). I've been with this project since the beginning a few years ago, using it on all my sites, and they just released the first real version last month.
http://communityserver.org/
I would recommend another year before it might be ready for the real public, as currently it's mostly a bunch of .NET programmers using it on their sites. Anyway, I do love it, I can play with the source code, and the community has forums, photo gallery, blogs, files, all kinds of toys for geeks like me!