If you are on Oracle you can use the chat module that's in the system. If not, do a search https://openacs.org/search/search?q=chat+oacs+ and you get just about everything that's been said on the topic.
Or if you have an irc server running on your system you can use the simple irc-applet package that I just committed to CVS contrib: openacs-4/contrib/packages/irc-applet (on HEAD).