SmackTop is an open-source utility for Mac laptops (after 2005) which translates the accelerometer (Sudden Motion Sensor) data into MIDI data and audio impulses. This enables you to control your favorite DAW by tilting and smacking your laptop.
SmackTop has two types of controllers - Tilters and Smackers. Tilters translate the left/right (i) and forward/backward (j) tilt of the laptop into MIDI CC values. Smackers use the change in acceleration (jerk) to trigger a MIDI CC, noteOn and/or audio impulse. The audio impulse is designed to trigger 'sidechain' effects.
SmackTop was built with Processing and Chuck. It is licensed under GNU GPL 2.0, although the included libraries are subject to their own various GNU or CC licenses. I am looking forward to getting other developers involved in this project - please contact me if you are interested. There is a lot to improve upon here...the code is generally ugly and slow (because I am a hacker and not a Java developer).