The SO-666 is a feedback based drone synthesizer. It is based on the earlier SO-KL5 piano synth.
By adding variable feedback to the strings instead of a single noise pulse you can create howling and screaming drones.
To be honest I was not yet able to find any musical application for it. It often sounds very dissonant and unpleasant.
But maybe that just what you are looking for...
Since it can be complicated to get any sound from this thing whatsoever you can try this:
Single notes and chords played while changing the cutoff, resonance and feedback.
No external FX or EQ.
Warning: May contain traces of melody!
Needs JACK and ALSA to compile and run.
Updated to version 1.01 with minor bugfixes.
License: GPL V3.0
Source on github: https://github.com/50m30n3/SO-666
Jeremy Salwen did an LV2 port of my synthesizers.
It can be found here: https://github.com/jeremysalwen/So-synth-LV2