Momentum is a new peer to peer (P2P) collaboration application that's a showcase for Swing and for what's possible using the JXTA support for P2P networking. The Momentum application supports sharing and collaborating on documents and drawings using email, chat, and direct manipulation. And there's no need for a special centralized server - all communication is peer to peer.
It supports both P2P and client/server architectures. Also has WebDAV support.