My buddy Brad Neuberg has put out a major new release of P2P Sockets to include improvements in reliability, performance, and documentation.
P2P Sockets is an open source framework that makes it much easier to create peer-to-peer applications. The basic goal of the project is to return the end-to-end principle to the internet. Users stuck behind a Network Address Translator will delight in P2P Sockets' ability to transparently traverse NAT. In addition, P2P Sockets uses a domain name space that is completely decentralized and not controlled by VeriSign or ICANN (Keep in mind this experimental domain name space is not secure and still relies upon "nice" clients to avoid collisions).
Are you eager to serve into a peer-to-peer network? It even comes with versions of a webserver (Jetty) and a wiki (JSPWiki) that have been hacked to run on the P2P network. See Brad's release post for more information.