Quassel IRC is a modern, cross-platform, distributed IRC client
based on the Qt framework.  Distributed means that one (or multiple)
client(s) can attach to and detach from a central core that stays
permanently online.  Re-attaching your client will show your IRC
session in the same state as you left it in (plus whatever happened
while you were gone), and this even when you re-attach from a
different location.  An optional Beginner's Mode completely hides
this feature, so Quassel IRC can be used like a traditional client.

WWW: http://www.quassel-irc.org/