Basically it would be a chat room where members could talk in real time. It's free, simple, and independent. It is somewhat like instant messengers (AIM, Yahoo!, MSN), but better in many regards.
In order to use, you will need an IRC client (MIRC, XChat, IRCSS, etc). There is also a firefox extension available:
https://addons.mozilla.org/en-US/firefox/addon/16 As an example, you can connect to the server irc.freenode.net and join the channel #alembic (command: /join #alembic) which I have set up for people to check out.
If you want to know more,
wikipedia is great.
(Message edited by juggernaught on September 16, 2007)