AJAX Emacs. If this doesn't excite you, nothing will.
Anyway, Emacs users, there's now a very neat AJAX implementation of your favourite text editor! It's called Ymacs and it only works in Firefox at the moment, but its list of Emacs-like features is impressively long! It's not an official port of Emacs, but the developer has faithfully preserved a lot of Emacs's commands and behaviour. There are split-screen windows, multiple file buffers and all the usual string operators, amongst other stuff. You can see a complete list of the commands in the Ymacs User Documentation.
It's all open source and free to use, or set up on your own server for whatever cool uses you can come up with. Having seen this, I'm rather interested to see what other console-based Unix/Linux apps have successful AJAX ports!
Go have a play with the Ymacs Demo! (but really, if you've never used Emacs before, start with the documentation)