InstantMessengers with Jabber support:

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GTK/GNOME : ** Gabber for GNOME (uses GTK) ** Gaim, a multiprotocol GTK2 InstantMessenger which has a Jabber plugin ** Gnome Jabber, a newcomer which is full of GTK2 goodness. (The web page says that the author has stopped development of this and is working with the Gossip authors.) ** Gabber2, the GTK2 port of Gabber. Still in development. ** Gossip, another GTK2 Jabber client ;
Qt/KDE : ** Psi, the canonical Qt client ** Kopete, KDE's main multiprotocol IM client. ** Konverse for KDE. Webpage was last updated in 2001. ;
Console : ** imcom for console (requires Python) ** jabmsg batch-mode Jabber message sender (requires Perl) ** CenterIcq, a multiprotocol Curses InstantMessenger which has a Jabber plugin ;
MicrosoftWindows : ** Exodus for MicrosoftWindows ** Jabber.com's client for MicrosoftWindows. (Current version seems to only let you connect to Jabber.com's server) ** JAJC for MicrosoftWindows ** Rhymbox, MSN Messenger for Jabber. Looks really nice in Windows XP ;
Others : ** Tkabber, written in TCL/Tk (requires a couple of extra TCL libraries) so this should run on any OperatingSystem that TCL/Tk runs on. It's UserInterface sucks, but it's very feature complete. ** Nitro for MacOSX