Here is a very tiny device with 13 mm height, 30 mm width, 76 mm depth, and a weight of 45 grams (final dimensions: 0.5" x 1.2" x 3"). With the Leap Motion software running on your computer, just plug the controller into the USB on your Mac or PC and you are ready to go (without any external power source).
Here it works with what it finds above it, capturing the individual movements of your hands and fingers in almost real time (200-300 fps) and translating the gestures into different actions on the application running on your computer. Launched in 2013, this $79.99 device is called the Leap Motion controller.
From the developer's point of view, this device allows designing applications that can be controlled simply by gestures and movements of the user's hands and fingers, just like in Minority Report!