I've been playing around with the Leap Motion Controller which tracks the position of the hands and fingertips by displaying a grid of infrared dots and looking for their change in position. In doing this it is able to give real time updates of hands, fingertips, position in X, Y, and Z as well as velocity, roll, pitch and yaw. Pretty cool with some interesting applications.
In working with some people at a hackathon this week I worked with a neuroscientist doing research in motor control and memory to develop an application to apply sound to physical movement. As a corollary of this and some interesting reading in college on the application of binaural beats, a different sound frequency played in either can affects the brain waves and can help to create certain mental states like meditation, relaxation, attentiveness etc, I created a Leap Motion controlled binaural beat machine.
The right hand, placed first over the leap controls sound in the right ear, while the left hand controls sound to the left ear. Or you can turn off the hands manually set a frequency.