Scroll pages by using hand gestures in front of a webcam. Useful for people who find fine movements painful (ie arthritis sufferers).
It's only for Mac at the moment, but should be easy to port to other platforms - only the key generation needs to be rewritten to use X11/Windows.
Written in the Qt framework.
You'll need opencv. To get it with MacPorts:
sudo port -v selfupdate sudo port install opencv