Basically, the ATTINY is pretty cool.  I love making small one evening circuits that I can put on a breadboard, sample a bit and tear it down when I'm done.

For this project, you really just need the ability to program attiny chips, a bread board, wires, pots, leds and perhaps a few ways to HEAR the sound.  I can touch on a few of those, but really, I will post links for that.

From there, just mix and match components like you would a modular synth.
I have created a few "convenience" tools, but really, I just tend to get an idea and throw it at the breadboard.

Here are some samples:

Sample 1
ACS-85-0210 is a delay like vco. Really, it puts the pot values in a buffer You can adjust the spread.

Sample 2

Here is 0012 ( like psycho lfo) driving a VCO that plays root/5th/octave...with a spread

Sample 3

0005 ( VCO ) driving an xor 0305

Sample 4

Sample 5
Chiptone VCO

## Similar works

MiniMoSynthA Formfactor and open source/open hardware design to make ATTiny Blocks.  Certainly the closest to what I have here.  I do not really have a
consistant strategy nor a consistant input like these little
blocks.  Check em out.

Rad-fi System from Bleep Labs Uses Arduinos as building blocks for Synths on a breadboard. A collection of ATTiny micros with these sketches would be completely compatible with this system.

Bastl Kastle uses 2 ATTiny85s that can be programmed with other features.

Electric Druid has some AVRs and others as building blocks.  For example, an LFO.

Moffenzeefmodularhas a project called MSG.  One of these sketches has made its way into that.  Neat!  If your not solder/hardware inclined, just get this and stick that that form factor.  Looks solid, if its not sold out.