Opera ha just announced Opera Unite: a web server that run inside the browser and that will offer functionalities similar to Google Weave.

Who will win the real-time web war?

Simply Wonderfl, that site allows to write as3 code directly from the browser and compile the result, while other users are able to see it and fork it to create a new version. Like a flash demo scene on steroid.
Inestimable for finding nice effects for flash.

Some interesting examples:
Clouds rendering
“Dune” like desert generator
Retro avatars generator
Water ripple effect