MacIRC

IRC stands for 'Internet Relay Chat'. MacIRC allows you to connect to IRC using your mac and talk to hundreds of thousands of people worldwide. On IRC, you are known by your 'nickname' and can talk to people who are in the same "channel" as you (each channel is like a virtual room, and each has its own topic - you can be in more than one at once.)

MacIRC is available in both 68k and PPC format