Before the release of Google Talk there was some speculation that it would be a browser-based program that worked via slick AJAX tricks like Gmail. Unfortunately that wasn't the case, but it was only a matter of time before someone else gave it a shot, and ajax im is the first up to the plate. It's pretty basic, but works as advertised. Everything happens in the browser via JavaScript and XMLHTTPRequest, and it has a few features like away messages. Probably not ready for prime time, but a great proof-of-concept (though it only works in Firefox and Safari).