I came across Pligg, open source community platform at the moment in beta, a while ago but lost sight of it (that will teach me not to blog it in the first place! It looks quite good and the best thing is the licence lets you use it for free and change the software as you see fit.

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the Affero General Public License is intended to guarantee your freedom to share and change free software–to make sure the software is free for all its users.