Penguin

Gaim started out as a GNOME AIM clone, but has since grown to become a multiplatform, multipurpose IM client. Since version 0.60, it is based on GTK2 and thus has full internationalizing support.

It even works on MicrosoftWindows through the GTK2 port for Win32.

The name of the Gaim project has now been changed to Pidgin and libpurple.