The Voice of Saturn synthesizer modules are available as basic (and bendable) complementary kits with control voltage connections.
Description of the VoS synth –
Loosely based on the Atari Punk Console with some custom tweaks and an LFO front end, this box makes a ridiculous amount of different sounds (mp3 coming soon), all from three 555s. Watch the video or download the mp3 for some samples. Comes as a bare-bones kit, an everything-kit with knobs and case, and a fully-assembled and tested version. It’s open source and has small area on the pcb for easy circuit bending. Skill level: Beginner / Intermediate
Weird sound generator kits
In the Maker Shed:
Arduino Pocket Piano Synth Kit