Here’s an interesting open source project on Kickstarter the Lo-Fi SES (Sound Entertainment System) by Assorted Wires:
The Lo-Fi SES (Sound Entertainment System) makes the process of playing an instrument easy by providing a video game controller interface for the lo-fi instrument. The d-pad allows you to change or record tracks, the buttons play the various sounds, and the l/r dials dynamically effect the frequency of the sounds as you are playing them.
A combination of things make this instrument unique. It is a fully open (hardware and software) audio platform, compatible with the Arduino ecosystem, and uses an innovative cart-based expansion system. Yay cartridges!!! The instrument is super approachable for level 1 musicians, but it is designed to be fun no matter what level you are at. The higher-level users can hack on the software via a “USB: a Link to the Hack” cart or even design a custom cart themselves. (I have a strong desire to see someone create a ridiculous rumble pack. You could make it rumble to the beat for some superfluous haptic feedback.) Also, the USB cart solves a common complaint for other lo-fi instruments: it allows you to swap out the sounds with ones of your own design!