This is a model of a 7-cylinder radial engine, a type of engine used in some early airplanes. (Not to be confused with the "rotary" engines used, unsuccessfully, in Mazda cars some decades ago.) Radial engines are basically the same as normal piston engines, except that the pistons are all arranged in a circle around a single crank arm, rather than stacked along a crank shaft with a separate crank arm for each piston. These engines are not used anymore, but they are very elegant, and they make a particularly nice model because all the action happens in a single plane.
Look carefully and you will see that one of the connecting rods is different from the others. Why? Because one of them needs to do the job of keeping the "spider" in the middle from trying to rotate out of place.
This is a high-quality model, made from laser-cut clear and colored acrylic. It will not run on actual steam or compressed air, but you can make it spin by pushing and pulling on the piston with just the right rhythm. The kit includes everything you need, even a mini-screwdriver. Assembly time is around 10-15 minutes.