The Wankel rotary engine was originally conceived as a supercharger, a purpose for which it is better suited than may appear on first glance. The rotor moves at only 1/3 crankshaft speed, meaning it can operate at high speeds, while it fills a chamber once each crankshaft revolution, meaning it breathes like a four-stroke engine of twice the displacement. Furthermore, it provides internal compression for theoretically efficient operation. The Wankel was used successfully, if not widely, as a supercharger before the focus changed to using it as an engine, and any surviving examples are most likely to be found either in a museum or slowly fading away in some German barn.
It was used to supercharge the little 50.
Have a nice Easter.
Sam.
