(2004-11-30) Gaim

GAim is an Instant Messaging client that runs on multiple platforms and supports multiple protocols - AIM, Yahoo, ICQ, and Jabber!

Downhill Battle is encouraging people to build an extension to support P2P File Sharing on top of it.

Update: I'm using GAim now as my client. Yahoo isn't blocked, Jabber is even working! (Though jabber.com seems dead, so I made a new account for seitz@jabber.org)