Gabbly Chat is an Ajax project that lets you chat with the visitors of any site in real time. If you add http://gabbly.com in front of a URL, the page will load, along with a small chat window where you can talk with other fellows.
You can use HTML code, including embedded images, links (spammers are probably thrilled).
In 3 hours after being submitted on Digg, the site was dead, which means their servers weren't ready for too many users. The site quickly recovered.
The concept is interesting: a webmaster could talk to the visitors of his site on any page, visitors could see other opinions about products, but on the other hand, it can simply become an Ajax IRC - full of spammers and teens that say "hi" and "ASL PLS".
Warning: the chat may contain explicit images and words.
Let's chat: http://gabbly.com/googlesystem.blogspot.com