There is a Jabber package, but I do not know of anyone actually using it in production. IRC is an option: an irc logger is running on this site. https://openacs.org/irc/
There is also an old chat package, which runs on OpenACS 3.x. Maybe someone has ported it?
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).