If you have a modern portable Mac, it’s likely equipped with Apple’s (SMS) Sudden Motion Sensor technology that is designed to protect the hard drive in the event of an impact.
As it turns out you can do a lot more then save hard drives with this sensor. Here are some apps that creatively use the sensor data for fun.
Classic arcade game that utilizes the sudden motion sensor to steer.
OS X 10.5 and later.
Turns your MacBook into a seismograph, measuring acceleration in 3 axis.
OS X 10.4 and later
Tilt SCREAM Pong
Pong, with screaming.
Security system app that sounds the alarm when it detect motion or other input. Armed with the Apple remote. Very customizable, can even send email, or run custom scripts if triggered. But note it isn’t perfect, a computer savvy thief will likely find a way around it. (e.g. plug in headphones)
Creates an aquarium on your screen. Water particles react to computer motion as if it were a liquid.