It’s the Nintendo synth that never was: a music keyboard accessories for the NES built as part of a 1984 prototype called the Nintendo Advanced Video System (AVS). Best features: a space sound and rhumba button. The one and only model is here in NYC at Rockefeller Center’s Nintendo World Store, which features various one-of-a-kind Nintendo items; see NES Central’s extensive gallery for description and photos by someone who actually knows how to take pictures (read, not me, as you can see).
I’m not sure any of these controls were actually hooked up to anything software-wise, but you can dream. Anyone want to build a keyboard for your Game Boy music system? More pictures after the break. (PS, Happy 20th Birthday, Mario! Just 1 year before we can take you drinking.)