FUTURERETRO'S Mobius is NOT a 303 clone, so why is it presented here ? Just because Mobius is the perfect companion to all hardware clone with midi/cv-gate which doesnt feature any built-in sequencer.
Mobius is the sequencer part of the world famous FR-777 in a rack, and can sequence in a pure TB-303 fashion any synth via midi or CV/Gate standards.
More info can be found at Future Retro's web page: http://www.future-retro.com