The are called shout-boxes. One such example can be found here
. However most boards that I use have MyBB so I'm not sure on the compatibility or how good it is.
There is a bot that allows for multiple users to chat to one and other on Windows Live Messenger without revealing email addresses. I use it with several other different forums and it's great. An admin can sign up here and post the address here. The site is Messenger Group Chat