Meet the Michel opposed piston engine in its original form.
Opposed piston designs were quite common early in the 20th century, but Herr Michel’s design took an unusual design and made it deeply and satisfyingly weird.
As an alternative to to pistons meeting in the middle, he thought of three meeting at a central combustion chamber. Not odd enough for you? His first design didn’t have a or any crankshaft. Instead each of the pistons had a roller attached to it which travelled along what could best be described as a wavy track, with the waves corresponding to the reciprocation of the piston. Depending on taste, you could have a fixed block with the wavy track rotating around it (the two piston model) or the opposite, a fixed track and rotating cylinders, used with three pistons.
Either way each cylinder could fire up to six times per revolution.
Later on he went more conventionally with crankshafts linked to each of the outer cylinders but they were never produced in significant numbers.