A bit more powerful than Arduino, but compatible with Arduino: Sanguino.

An open source 8-bit game console (an Uzebox successor)

AVGA is TILE-based AVR interrupt driven audio-video driver for a single-chip game console. Or: It's a great board for developing and prototzping AVR video stuff!

The Uzebox(tm) - a retro-minimalist homebrew game console.

The MP3 player does not have any buttons nor dials that shown in right photo and it has an acceleration sensor instead of the mechanical switches. Therefore all playback commands to the player are given in defined motions, such as inclination, tilt and shock. The player detects the motion with the built-in acceleration sensor and recognize it as a playback control command. As the result, it came to not seem an audio player in appearance.