Bumpy is a minimalist DIY MP3 player with 3d printable case developed by Matt Keeter. It plays MP3s from SD card and it's open sourced. I've been thinking about getting rid of my smartphone, buying a dumb-phone and using stand-alone MP3 player and this looks very interesting.
The case is printed on Formlabs machines, but you could also probably do it on other 3d printers:
You can find all the information about Bumpy and how to build it here: