I came across a service called Gabbly. It uses Ajax to add a chat widget to a website which can then be used to facilitate chat between fellow-gabblers.
For example, the code to add to my website at http://yeda.cs.technion.ac.il/~yona/ is as follows:
<iframe src='http://cw.gabbly.com/gabbly/cw.jsp?e=1&t=http://yeda.cs.technion.ac.il/~yona/' scrolling='no' style='width:300px; height:250px' frameborder='0'></iframe>
Of course, you'll need to register with them, i.e., give them a username a password and an email address, which they validate using a link they email you and expect you to click in order to invoke the account.
You can also initiate a chatter on any website from their site simply by entering a URL into a form and clicking submit.
Another nice thing I saw was an ability to get an RSS feed from a chatter box. I couldn't think of a use for this -- but it does look like a "cool" feature.