Not entirely dissimilar to the 2008 patent which showed an iPhone being controlled by camera-based input, is this German student's app, which controls the Maps app being controlled by the camera tracking hand movements through the app.
It's probably easiest if you watch the below, which demonstrates—in a slightly limited fashion—a hand being moved in front of the camera, controlling a dot moving around the iPhone's Google Maps app. The iPhone is connected to a laptop, which has the Map interface displayed. Interestingly, moving the hand further away from the camera zooms the map out, and moving it in zooms the map in.
I can't see how this app could be used any further though—or maybe I'm being too obtuse? The idea of having another way to control a touchscreen phone just seems a little crazy to me. [Daniel Bierwirth via Recombu]