This is a low temperature hot air engine. Ross Yoke is the name of the special linkage used for deriving the required 90 degree phasing with a single crank. It has a large area displacement cylinder, which is intended to be heated by standing on a cup of hot water or a similar heat source.
The displacer constitutes the base of the engine and is 100mm diameter x 15mm high. The displacement piston is made of light weight foam material. The top and bottom plates are made of transparent plastic (presumably Perspex).
On the top plate is mounted the support pillar for the flywheel and linkage, and the aluminium(?) power cylinder. The power piston is 13mm bore x 8mm stroke. The crankshaft has a single crank which is connected to the power and displacer pistons via the Ross Yoke linkage (see the video for how this works). The flywheel is 118 mm diameter and of lightweight construction. Despite it's light weight, it gives the engine a very smooth action.
The engine works well sitting on a cup of tea or a block of ice, although it won't work by the heat from a hand, like some will.