SpaceChem (2011)

Program moving manipulators to pick up, join and separate atoms, then make several reactors cooperate in a production line. A collision or blocked output gives a visible symptom to investigate, and different layouts can satisfy the same brief. Its chemistry operates as a set of puzzle rules, with the later challenge coming from coordination and throughput. This is a demanding choice for someone who enjoys tracing the consequences of a small local change across a much larger machine.