When Apple released iOS 4.2 end of last year I was on a boat trip to Finland. For me the most interesting features were added to Safari browser. I wanted to learn about WebSockets. New DeviceOrientation API just begged to be abused. I had an idea to control the content of laptop browser by tilting and rotating the phone. I had working but ugly code before ship arrived to Helsinki.
If you have short attention span go straight to the HTML5 logo demo.
Code has been sitting on my hard drive since. I cleaned it up during last couple of days. Also added additional eye candy by using the oh-so-hot-at-the-moment HTML5 logo.
Previously I experimented with drag and drop file upload with Google Gears. Recently FireFox 3.6 (codenamed Namoroka)
Correction: Ionut G. Stan pointed out that File API was actually available already in FireFox 3.0. What Namoroka introduced is the drag and drop interface for the files. Sorry for the confusion.
old new HTML5. Again there is a working demo. You will need FireFox 3.6 to test it. Full source code can be at GitHub.