Best Web demos?

The Mozilla Evangelism team is looking for the best Web demos we can find. We’re putting together a collection of these to show what today’s Web is truly capable of — from offline Web application support through text animation using canvas and more. If you have or know of a demo that really shines as an example of modern Web capabilities, please leave a comment and a link. Thanks!

Update: Bonus points for demos that show off the new content-related features of Firefox 3.