Alexander Ryzhkov created a small 555 timer-based 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:
Here is a video of the board in action:
openidev has shared the board on OSH Park: