You can find a video of Kasper going crazy on the little synth here: https://youtu.be/Kh5FDFdGQUs
The arduino comes with the firmware installed but if you are a programmer and want to tweak the code: the code is open source and you can download it here.
The arduino NANO in the kit is provided with a CH340 ic and to communicate with your computer you need to install a driver. In this link you can find the drivers: https://sparks.gogo.co.nz/ch340.html.
Documents:
Download the firmware here: mini-synthV1.zip
Building manual/BOM: LITTLE SYNTH building manual v1.pdf