Facebook/Gmail like collaboration chat

I got a WP website with multiple authors, and just thought of how great it would be if there was a instant chat feature for logged in users (lets say everyone above a certain user level). Like a list on whos online just like in facebook or Gmail, and option to send direct messages.

That would be SOOO cool. Anyone heard of this feature? Maybe there is a plugin I havent seen? Or do you think it’s possible to implement?