The Chat Room tool allows you to carry on real-time conversations with site participants who are signed in to Sakai. All chat messages are saved, and any site participant can read them. You can use Chat Room to set up online office hours in which to answer student questions, and then make those answers available to all students. For project sites, Chat Room allows dispersed colleagues to communicate and keep on conversations they may have missed.
Search here for how-tos on the Chat Room tool.