IM Client for Mac OS X

Adium X is a multiple protocol instant messaging client. It now utilizes libgaim (the core part of gaim) to connect to multiple protocols, and is also based on a new plugin architecture. Partial address book integration, cool looking tabs, multiple protocols for instant messaging, and a compact contact list are some of the many features of the new Adium X. Adium supports AIM, ICQ, MSN, Yahoo!, Rendezvous, Yahoo! Japan, Gadu-Gadu, Jabber, Napster, Lotus Sametime (via the Meanwhile plugin), and Novell GroupWise.

Fire is a free Instant Messaging client for Mac OS X. It supports the seven most popular Instant Messaging services: AIM, ICQ, irc, Jabber, MSN, Yahoo! Messenger, Apple Rendezvous