OpenKinect is a library that interfaces the Kinect camera made by Microsoft for the Xbox to Linux, Windows and OSX. This library has multiple overlays and effects that take advantage of the way the Kinect works by being able to manipulate the video feed from the standard video camera in the Kinect by examining the 3 dimensional layout of objects in front of the kinect from the infrared camera. The third circle on the front of the Kinect is an infrared emitter that emits a matrix of dots whose distance is visible from the infrared camera producing a 3 dimensional layout of the objects reflecting the dots.
OpenKinect software can be downloaded from the OpenKinect website here.