Pidgin is an instant messaging program for Windows, Linux, BSD, and other Unixes. It works with AIM, ICQ, Jabber/XMPP, MSN Messenger, Yahoo!, Bonjour, Gadu-Gadu, IRC, Novell GroupWise Messenger, QQ, Lotus Sametime, SILC, SIMPLE, and Zephyr. Pidgin can log in to multiple accounts on multiple IM networks simultaneously. It works on numerous operating systems, including Windows, Linux, and Qtopia. A similar program for the OS-X is Adium, which can be downloaded here. The latest stable version of Pidgin can be downloaded here. The latest BETA version of Pidgin can be downloaded here. More information here.