Hybrid and Alternative Propulsion Systems

Propulsion systems built around an alternative to a conventional single internal combustion engine: hybrid-electric powertrains, battery-electric drive systems and hydrogen fuel cell propulsion, a distinct and fast-growing engineering category cutting across the vehicle domains above rather than filed under any one of them. Belongs here: any named hybrid, electric or fuel cell propulsion system of real engineering or historical significance. Does not belong here: a conventional piston or turbine engine, tracked under its own vehicle-domain bucket above.