OSNews mentions an "AJAX operating system" called AtomicOS. I wasn't very impressed with their version of a terminal, especially when there is a far superior implementation - the JS/UIX terminal which feels much more like a real terminal.
Most AJAX / Web 2.0 applications really don't impress me. If they did I wouldn't be working on Vexi. HTML is a documentation tool, at best a presentation tool. As nice as applications like GMail have become, they'll never be able to match real GUI applications.