The theremin is an electronic musical instrument, the oldest known that does not involve physical contact of the performer with the instrument. In fact, the sound is obtained by waving the hands near its two antennas.
Open Theremin is an Open-Source hardware implementation based on Arduino Uno. Together with Arduino, a Shield was built in which there are 4 potentiometers and the connections for the two antennas. For those wishing to replicate it, Gerber files are available for free.