Klaus Weidenbach
A P2P-based social network framework by the University of Paderborn
Forgot to visit them at CeBIT. I think they are already working/researching since 5-6 years, but they still don't have public available code.

P2pframework: A Toolbox for Building P2P-based Social Networks

Enormous application range, secure and competitive, no operating costs Digital social networks promise to activate the social participants and to support them in their interactivity patterns. Private relationships evolve to friendships, professional contacts define competence networks and political opinions emerge to revolutionary trends. Social ne...
Fabio
server is down..