Atomcraft A whole planet as your chemistry set

Pick up any pixel and place it somewhere else. That is the whole foundation, and everything grows from it: pixels react to their neighbours, so heat meets ore and something melts, acid meets metal and something dissolves. You dig into the planet with an upgradeable drill, hunting better materials the deeper you go. One moment you are smelting a batch of ore in a steel vat; the next the sulfuric acid you just made eats through the vat and spills across the floor, and you are improvising a glass container instead. The simulation does not care about your plans, which is exactly the fun of it.

There are no prefab factories here. You design machines pixel by pixel from mechanical parts: conveyor belts, trapdoors, heaters and coolers, wiring, buttons, switches, sensors and logic gates. The game tells you what ingredients a reaction needs, but not how to arrange the plumbing, so working out the machine is the puzzle. Some crafts raise the stakes: nitroglycerin needs a carefully built reaction setup, or the materials simply explode. When a contraption finally runs on its own, separating, heating and mixing without your help, it feels earned.

All 118 elements exist somewhere on the planet, and extracting them from their ores takes creativity rather than a recipe click. The reactions hew close to real chemistry, so playing teaches you things without trying: heat limestone with coal and it becomes quicklime, and suddenly you know where the phrase "in the limelight" comes from. A built-in encyclopedia lists reactions for the elements you have found, and the rest you work out by experimenting. Throw things together, burn things, see what happens. It is the kind of lab work no school would ever let you do.