Audun Mathias Øygard's creative experiment uses real-time facial recognition to hide your face in a webcam feed with different masks. That could be handy if you want to scare your friends with a real-time Nicolas Cage imitation (don't forget to use it with a proper soundboard) or just confuse them while playing online.
If you have a webcam, you can try it our for yourself here. Also, thank god Hatsune Miku is not included in the demo list. That would make things more frightening.