A couple Stanford grads have released a web-based, Ajax instant messaging client called
Meebo. It currently supports AIM, MSN, ICQ and Yahoo and works quite well for basic one-to-one text chat... and not much else.
You won't find bells-and-whistles, or even emoticons, at least not in this alpha stage. But it does work, even through a corporate firewall (at least until the IT guys start blocking access to meebo.com).
Meebo works pretty smoothly, although there appeared to be some glitches when I tested. Messages sent from Meebo over the MSN network were received fine, but my replies to the Meebo "client" opened a new chat window. They still got through, but communicating in two windows was awkward. Of course, it could have been complicated by the fact that the other party was actually using
Trillian Pro.
Overall, the Meebo interface is very clean and looks quite polished. They are collecting feedback via a
forum and posting updates on their
blog. If you need a web-based IM for basic chat, give
Meebo a try.