Bubblegym is, as far as I know, the very first computer game that reacts to how the machine is tilted. Many Apple laptops have a chip on the logic board that is there to signal if the computer is dropped. Thanks to Amit Singh (kernelthread.com) and Christian Klein, this chip's values can be read and utilized for your amusement. The gameplay is simple but challenging, control the balls by leaning the computer and get to the fruits before they disappear.
The program is donation-shareware. Donate what you think it is worth and you get the full version.