The MAKERPad codebase.
The MAKERPad is MIDI fighter pad inspided LED button matrix. The LEDs use charlieplexing to reduce the number of pins required.
Just click download zip on this repository and then in the Arduino IDE Click Tools -> Libraries -> Import and select the zip downloaded.
The idea for the multiple buttons on one line found at: http://forum.arduino.cc/index.php?topic=8558.0
