A universal instant messaging (IM) program
See https://pidgin.im/about/ for more information. Pidgin is an instant messaging program which lets you log in to accounts on multiple chat networks simultaneously. It runs on Windows, Linux, and other UNIX operating systems. Pidgin is compatible with the following chat networks out of the box: AIM, ICQ, Google Talk, Jabber/XMPP, MSN Messenger, Yahoo!, Bonjour, Gadu-Gadu, IRC, MXit, Novell GroupWise Messenger, Lotus Sametime, SILC, SIMPLE, MySpaceIM, and Zephyr. It is written in C and makes heavy use of GLib and GTK+. Finch is a command line instant messaging program. It also lets you log in to accounts on multiple chat network simultaneously, and it is compatible with the same chat networks as Pidgin. It is written in C and makes heavy use of GLib and ncurses.
emesene is a platform independent instant messaging client for the Windows Live Messenger (tm) network. emesene is distributed free of charge under the GNU General Public License 2 or any later version.
MSN/Live Messenger chat client for Linux.
KMess is an MSN/Live Messenger compatible chat client for Linux. The strength of KMess is it's integration with the KDE desktop environment, focus on Live Messenger specific features and an easy-to-use interface.