A common hacker upgrade to an espresso machine is to improve stability and performance with a better temperature controller ... It runs on an Arduino MEGA 2560 PRO (or similar microcontroller ...

To make a simple MIDI controller, you need knowledge of firmware ... circuit board that serves to break out the connections on an Arduino nano to a dozen arcade push buttons, four slide pots ...

This little hack project by Kellbot of NYCResistor takes a rolling ball, an optical mouse, a gutted PS2 controller, and some Arduino hacking and makes it into a working (and awesome) virtual Katamari.