Fire is a Free Instant Messaging Client for MacOS X which supports all of the most popular Instant Messaging services in one easy-to-use application.
Fire, from Epicware, is a freeware Multiplatform Instant Messenger client based off of freely available libraries for each “service.” Currently Fire handles ICQ communication, and Yahoo! Pager communciation. All “services” are built off of gpl’d libraries, including firetalk, icqlib, and gtkyahoo (linux libraries).
Fire looks somewhat like AIM, but does much more. It can handle similtaneous connections to AIM, ICQ, Yahoo , IRC, MSN and Jabber IM.
More info and download link here.