Today I went to a talk on a rather interesting piece of software named
Circle. This is a new, experimental peer-to-peer communication system with no central servers or points of control whatsoever, organised along the lines of a distributed hashtable.
It was designed by a PhD student at Monash University (where the (centralised)
Goofey messaging system originated a decade earlier).
The Circle client, which is written in Python, includes instant messaging, a decentralised news service based on trust metrics and file sharing/searching using the distributed hash table; it seems pretty interesting.