Opus Magnum is a puzzle game about assembling machines to convert spherical chemicals into different compounds. Each challenge can be tackled by creating different machine configurations, and each is awarded points on how compact, quick and efficient they are in terms of material used.

The puzzles follow an intriguing and dark plot that swirls around ancient city Houses. "Alchemists, who hold the power to create almost anything known to science, are highly sought— and highly dangerous."

The engines you create are represented on a grid of manipulation tools. These are mechanical arms that rotate around a pivot point, pick up and drop atoms, and move structures it currently has picked up. They combine with transmuters that create a bond, destroy a bond, transform a basic element into "salt", or upgrade base metals into higher ones using quicksilver.

This all sounds highly technical, complex and not much fun. But the genius of the game is how elegant it is to play, and how the interface lets you experiment, learn and iterate complex solutions without deep chemical knowledge.

The game enables you to create your own puzzles, provided you can prove that they can be solved.

This is one of a series of games by a developer called Zachtronics. He makes these games free for use in schools and education.