Hacked Gadgets uncovered this device, which is built from scratch by an Japanese engineer calling himself ChaN. The MP3 player uses a three-axis accelerometer, enabling it to sense tilt, inclination and shock. The device features no buttons, and has a SD card slot, and a small, 2.1w speaker for playback. Plus it has an audio jack to attach a second speaker.
If you turn the player so that the speaker is face down, it turns off; lift the speaker side off the table and it back on. If you tap one of the corners against the table, it will skip forward a track. Tapping the corner on the opposite side will make it skip back a track.
You can also roll it on to its sides horizontally adjacent to the speaker to increase or decrease volume. Obviously, for some of these controls, buttons seem easier, but it's a cool demonstration of what you can do with simple technology and a good idea. [ELM via Hacked Gadgets via Dvice]