The Wii system has shown promise in health applications (USA Today Article), and so has Dance Dance Revolution (New York Times Article). Project Natal promises to have a larger application than these two platforms because the games will no longer require a controller and will allow the user a greater range of motion.
So far there is not a release date, but it was demoed on Late Night with Jimmy Fallon in Jun. Click here to see the demo.
Compatible with any Xbox 360 system, the "Project Natal" sensor is the world's first to combine an RGB camera, depth sensor, multi-array microphone and custom processor running proprietary software all in one device. Unlike 2-D cameras and controllers, "Project Natal" tracks your full body movement in 3-D, while responding to commands, directions and even a shift of emotion in your voice.
In addition, unlike other devices, the "Project Natal" sensor is not light-dependent. It can recognize you just by looking at your face, and it doesn't just react to key words but understands what you're saying. Call a play in a football game, and players will actually respond.