Once you raised your questions, @Paul-Chambers, my seems to fit even better as I believed.
I am facing the following problem. Since our forum is sport related there tends to be lot of communication during game time (aka: Ooh what a monster block). We would like to move those shouts into a chat. Other as shoutbox or global chat everybody should be able to sign in or out to that chat by his own.
So my question seems to come down to:
I am not absolutely sure, but I believe I saw the possibility to create a chatroom using the API in one of the above mentioned plugins.