Okay, this one is in German, but I'm sure you can find similar stuff in most other languages , like this...
As you may see, all this is based on the Arduino Micro Controller - and this is a pretty cool thing! It's a little computer with analog and digital connectors, so you can add almost any kind of dials, switches, sensors, displays etc. And as it's a computer, it needs to be programmed, but this seems to be pretty easy (there are a lot of tutorials available) and can be done with any PC, Mac or Linux machine.
I just got my Arduino starter kit containing a bunch of weird stuff for just 42.99€!
Let's see, what I'll build with that ...
BTW: The guy in the German video above just started a new series on how to turn a Korg Monotron into a serious synth using the Arduino .