TAFFI (Thumb And ForeFinger Interface) is, in the words of its creator, “an inspired hack”. Andy Wilson of Microsoft Research wrote an algorithm that uses a cheap USB camera connected to his PC to allow him to control the computer with his hands held over the keyboard. No mouse or other pointing device; the software simply recognizes when his thumb and forefinger close together to make a loop. Watch the video in the link above, or here.
I’m no programmer, but this just strikes me as brilliant. Simple and brilliant.
A pdf of Andy’s paper on the subject – "Robust Computer Vision-Based Detection of Pinching for One and Two-Handed Gesture Input” (catchy title, eh) – can be downloaded here.