Artists usually place a hidden track or two in their albums. The upcoming three EPs of electronic artist Captain Credible on the other hand will each have a randomly generated track.
The Dead Cats EPs are based on an ATtiny85 microcontroller and Captain Credible’s Arduino sketches. The power switch is embedded in the 3.5mm input. The generated track is practically infinitely long, but once generated you can restart the song by removing and then reinserting your 3.5mm jack into the board.
Each circuit board will also come with a digital download for the rest of the songs in the respective EPs. You can order the first Dead Cats circuit board EP from Bandcamp for ~$18 (USD). You can download the Dead Cats source code and Gerber file from Captain Credible’s website.