Bubblegym is to my knowledge the first tilt-sensitive game for notebook computers. When Apple revised their Powerbook line earlier this year, they added Sudden Motion Sensor (SMS), a detector that is used to protect the hard drive if the machine gets dropped. Chances are, they probably weren't expecting it to be used as a video game controller...

Bubblegym utilizes the SMS (Sudden Motion Sensoring) system built in to the latest Powerbooks. The SMS system is there to lift the reader from the hard drive's track if the computer was dropped or suddenly shifted. The actual sensor is a chip built into the logic board. Thanks to Amit Singh (see below) the values can be read and used for things like this. How the sensor chip works? I dunno... A little person inside or something?