vbmessenger?

[TigerC10]

I think this is as close as you're going to get.

You should also look into shoutboxes, some can be detatched from the window in the way that the messenger I linked you to could. They can also be put on their own separate pages to achieve a chatroom feel.



But as far as an application that people could download and install, a true-form chat program... I don't think there is one.