Bumpy is a small homemade mp3 player, with features similar to an iPod shuffle. The entire design is open-source, from the firmware to the circuit board to the 3D-printed case.
Bumpy plays .mp3 files off of a micro-SD card. You can load files onto the card then plug it into Bumpy, or plug Bumpy into your computer: it will show up like a flash drive (though it's a bit slower).
The UI is simple and minimalistic. A scroll/click wheel lets you change volume, play and pause, and move foward and back through your .mp3s. Eight LEDs glow through the case and show the player's status; eight-bit animations give feedback when you change songs.
Bumpy recharges with a standard USB-mini plug. With typical use, it will play for over 24 hours on a single charge.
Bumpy's firmware and PCB are both hosted on Github.