It's yet another quirky firmware project for the Arduboy! This time, you can use it to control playback on a Music Player Daemon (MPD) instance.
This project relies on a Python script running on the host machine, which will feed song information and relay button presses between the Arduboy and the MPD server. This will, unfortunately, mean that the serial communication LEDs will be constantly lit, but there are limited means of pushing data between the devices. At least it's not constantly blinking.
For more details and instructions, see the github page.