Sequential Circuits Six-Trak by syzygywell
First of all I love this synth. It's the little synth that could as far as I am concerned. It is underrated at this point and I think that is mostly due to the one dedicated knob for most functions on the synth which is its major downfall.
Polyphony is 6 with no aftertouch. No built in effects. No expansion. However it has full MIDI manipulation meaning real-time parameter control. It also has a very good onboard sequencer for a synth built in 1983.
In stack mode I can get some pretty huge sounds out of this little thing. It definitely has that sequential sound bright and brassy which is perfect for what it does. It has a bit of prophet 5 in it but not nearly as large or fat. However I love some of the silly sounds it makes as well. It has a sweet tone that is completely different from the prettiness of Roland gear made at that same time but complements it well. I use this in conjunction with my Juno 60 often.
Other than the sequencer it is definitely light on features and only has one vco per voice but its got a solid build and is a great synth for the price they are going for currently.