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This is a 4 x 4 matrix of illuminated pushbuttons with a two-wire I2C interface that you can use for games, music, or control applications. The circuit is controlled by an ATtiny88, and you can independently set the state of the lights, or read the buttons, via I2C. I've included a demo program for the Arduino Uno that uses the Button Matrix to play a puzzle game called Tacoyaki.

For more information see Illuminated Button Matrix.