The National Automobile Museum in Reno Nevada brought their 1906 Adams-Farwell Series 6 touring car to Pebble Beach last year. It’s the last car of it’s kind and it has the only working Adams-Farwell air-cooled 5 cylinder rotary piston engine in existence. Rotary piston engine you say? The crankcase with the 5 cylinders rotates around a stationary crankshaft in the center of the engine. The layout used centrifugal force to distribute fuel and scavenge exhaust gases while providing exceptional air cooling. I guess this is technically a rotary radial engine which is rad.
Source: YouTube user EarthAdvocate