The NovaDrone from Casper Electronics is an open source, analog experimental  sound a light synth. It's currently available as a pre-assembled board, PCB only, or PCB and kit in both single and double versions. Prices start at around $100 for the full kit, with a board only and a parts also available.

Here's the blurb

The NovaDrone offers 3 channels of sound and light.

 Each channel has the following features:
ADJUSTABLE CONTROLS
-volume
-TONE pitch coarse tune 24Hz to 750Hz
-TONE pitch fine tune
-LFO rate .008 Hz (around 1 cycle every 2 minutes) to 750Hz
SWITCHES
-sync 1
-sync 2
INPUTS
- ext sync 3
-PITCH modulation
-LFO rate modulation
OUTPUTS
-TONE square wave
-TONE triangle wave
-LFO square wave
-LFO triangle wave
-PWM square wave
-High current LED out for off board LEDs.

More Information

• Casperelectronics.com

• Superbooth 2018: Casper Electronics Feedback Mixer Prototype 04-May-18
• Superbooth 17: Casper Electronics/Bastl Instruments softPop Synth 22-Apr-17
• New DIY 4-Voice Analog Synthesizer 21-Oct-09