For some time already been planning to make a super simple FM module. Here it is, still one part is not working: simple VCA, to have more control over each voice for some more madness. Module contains 4 independent voltage controlled oscillators (CD4046 square wave osc). Decided to keep each voice separate for mix input, so it means it is possible to feed any other external signal and mix it in this way.
So it's basically few things in this module: 4 independent CD4046 voltage controlled oscillators and one CD4070 XOR logic gate. 4070 is super simple chip - you just feed two inputs and get one output. And with one chip you can have up to 8 inputs and 4 outputs (you can even feed one output to another input to get even more crazy wave shape. In this case I have 4 oscillators feeding into two inputs and then those two go into one, so you get kind of "7 wave shaping steps", but you can just switch patch cables and get a simpler mix, like using only two oscillators and mixing them into one output.
Plan for the future: to make a similar module, but instead of mixing VCO's - mix separate step sequencers to get a more complex rhythmic patterns.