And it works in an actual cassette player too! There are all the standard play functions and a head phone jack.
The music is stored on a separately sold SD card. It looks just like a real cassette tape too, with the two holes that you used to have to use a pencil in to wind the tape back in whenever it jammed.
The best part, in my opinion, is the fact that you can apparently pop it into a cassette player and it will work! This feature probably works similarly to those cassette tape CD player adapters they used to sell for hooking up your portable CD player through your cassette deck. They are cheap too, a mere $21.96 each, sounds pretty close to what you would probably pay for a blank cassette these days.
Cassette tape MP3 player [via Crave]