Nothing has more rare content than newsgroups but the stuff only lasts for a couple of days if you use your isp for usenet.
"Gnewsgroups trys to solve two main problems regarding Usenet and peer-to-peer applications.
Usenet is more and more frequently being filtered and censored.
Peer-to-peer applications are limited to simple search services.
How does it work?
Gnewsgroups is a peer-to-peer application for Windows. Its built on the open-sourced GnucDNA library. GnucDNA provides network support for the Gnutella and Gnutella2 protocols. Gnewsgroups implements Usenet in the Gnutella protocol by performing automatic searches for gnewsgroup and gnewsmessage meta-data"
http://www.gnewsgroups.com/