Wankel engine
The Wankel engine was first thought of by German engineer Felix Wankel in 1929. He started working on it in the early 1950s along with German car company NSU. Since, it has been used by various other car companies, but mostly in prototype cars. One exception was Mazda, which made several cars that used Wankel engines, with the most well known one being the Mazda RX-7. As of 2021, there are no cars in production that have Wankel engines.