One of the most ambitious projects I've seen in this vein is psyced ( http://www.psyced.org/ http://www.psyced.org/ ) which starts from a redesign of IRC and ha

One of the most ambitious projects I've seen in this vein is psyced ( http://www.psyced.org/ http://www.psyced.org/ ) which starts from a redesign of IRC and has gone on to accumulate a kitchen-sink's worth of protocol compatibility(from the front page: Jabber™/XMPP S2S, IRC, TELNET, HTTP, SMTP, OAuth, XML, RSS; limited/experimental code for XMPP C2S, Java Applets, Status.Net, Twitter API, WAP, NNTP.) The core protocol is a gorgeous "Right Thing" design which has had many years to mature, and attempts to cover all venues: IM, chat room, microblogging, mail, profiles... However, like with all of these open-source efforts, traction as a network seems to be missing.