[Michael] tipped us off about an incredible build from back in 2005. The Melloman is a keyboard that uses a different tape loop for each key. The instrument is generally known as a Mellotron, and consists of a different looping tape for each key. When a key is depressed, the head comes into contact with the key and plays the sound sample.
This particular implementation uses 14 Walkmans to supply the tape loops. The Walkman units are constantly playing but the audio output is not enabled until a key is depressed. The main description of the instrument is on the final project page linked above but there are many construction photos available in the build log.
Update: After the break we’ve embedded a video that will take you on a tour of the components of the Melloman. To clear up the looping issue: a Mellotron uses tape loops, but the Melloman uses tapes that are 30 minutes on each side instead of loops.