I made a thing! It’s a little 13 key capacitive touch sensitive 4 channel polyphonic piano. Not related to arduboy, other than tangential instances of touch sensors and polyphonic audio showing up in other people’s arduboy projects and that it uses an atmega as the microprocessor. It’s a gift for my sister who used to play the piano. Here’s a vid of it in action:
All design files are posted on the project page in the video description for those who want to make their own.