Alexander Ryzhkov created a small 555 timer-based piano:
555 piano
Main goal of this project has been creating pretty designed 555 based piano in small form-factor. Many 555 piano are using 9V battery for supply. I use CMOS timer and for timer need only 3V supply.
The design files are available on GitHub:
ChirnoTech/555Piano
Here is a video of the board in action:
openidev has shared the board on OSH Park:
piano.toplayer.zip
OSH Park 