A climax is a steam locomotive with and angled piston.
A Forney is a steam locomotive that has the wheel arrangement 0-4-4. A Forney is always a tank engine. This means it does not have a tender.
A gypsy locomotive is a tank steam engine with a large gear at the front, which was equipped with a rope and used to haul logs and other tasks.
A Heisler locomotive is a steam engine with the pistons in a V configuration on opposite sides of the engine cab.
A mallet is a steam locomotive with two sets of pistons.
A shay locomotive is a stream locomotive that has up and down pistons.