Internet Relay Chat is an early form of instant messaging with multi-user chat rooms called "channels." While its popularity has decreased since the early UNIX years, it is still use. IRC clients exist for just about every operating system and web clients are available in Java, Flash, and AJAX. Many varieties exist for the Macintosh, Windows, and Linux operating systems.
I am a member of the following IRC networks/channels
Below are embeddable widgets from
mibbit for these IRC channels. While they are quick and easy to use, I recommend getting a desktop client. If you are somewhat knowledgeable with the UNIX shell, I recommend
irssi, the client I use.