This is an engine powered by compressed air. It's made of wood and so can't be powered by steam. It came as a flat-pack kit of mainly laser cut plywood parts. It is held together partly with tooth picks and partly using a slot together technique. Tooth picks also form the shafts and rods.
The cylinder is a double acting fixed cylinder with a piston valve. It is 11mm bore x 11mm stroke. The valve linkage incorporates a bell crank which is operated directly by the main crank.