SynthGear – The Atari 400 Synth using „Pokey“
This is using the old Atari Pokey Soundchip but not the Rest of the Computer Hardware, so this is a real Synthesizer on/with Atari 400 like Midibox SID etc.
via this page (found me via twitter and I found this on their/his/her site):
SynthGear » Blog Archive » The Atari 400 Synth.