Minecraft

Minecraft hands you an endless procedurally generated world built from cubes and almost no instructions. By day you gather wood, stone and ore. At night monsters come, so you build shelter. From those simple rules people have made redstone computers, scale models of cities, and quiet farms to live in. There is a loose goal involving a portal to another dimension and a dragon, but most players ignore it. The look is deliberately crude, low-resolution textures on chunky blocks, and that simplicity is why a child and an engineer can both lose months to it. Markus Persson started it alone. It went on to sell more copies than any game in history.