Glitch, the gorgeous new game from Flickr cofounder Stewart Butterfield, runs Flash

From the Glitch About page:

What technology does it use?

(Heh. Nerd.) The game client is Flash (though someday there will be other clients) and the server is built in a fairly new and different way for a game: the back end (java at the lowest level, with game logic scripted in Javascript) is designed for maximum flexibility and ease of deployment. That means we’ll be able to push new content — new items, new places, new characters — on a daily basis. It also means that we have lots of APIs with which the game can be expanded and extended.

Rich games like this will probably be some of the last sites to move over to HTML5.

Related: HTML5 websites should complement apps, not aim to replace them