The SynthaSystem was produced by Steiner-Parker in the 1970's. It is a compact, expandable modular analog synthesizer system that didn't quite compete on the same level as the EML, Moog, ARP and EMS systems of the same time. But it deserves some attention. It's great for creating sound effects including thunder, wind, surf, race cars, sirens, horns, explosions, jet airplanes, "tunnel" sound processing, and many, many more. But when it comes to reproducing natural acoustic sounds...well, good luck. It claims to simulate piano, organ, trumpet, accordion, violin, oboe, drums, guitar and many more but most are pretty questionable.
But as an analog processor and sound design machine, the SynthaSystem shines. With up to 74 knobs and switches (or more) and its expandable modular design you can create some wacky noises! It can also be used to process existing sounds via an external audio input! Very cool for filtering stuff! The SynthaSystem may be uncommon but it can be an affordable alternative to similar synths.
Demos & Media
Thanks to Peter Grenader of Buzzclick and Arlo West for providing information.