ajax im is the name. It is AJAX Based instant messenger, I tested it on their demo site, it works pretty well except few bugs (It didn’t allow me to resize messenger window in IE 6)

Details about the messenger from their website:

ajax im (“asynchronous javascript and xml instant messenger”) is a browser-based instant messaging client. It uses the XMLHTTPRequest object in JavaScript to send and receive commands to and from the server. No refreshing of the page is ever needed for this “web application” to work, as everything is updated in real-time via JavaScript.

I might try it soon on one of my sites 😉