Terraria

Terraria is routinely mistaken for a Minecraft variant and is a substantially different game. Its world is finite and hand-generated in layers, its progression is gated behind bosses rather than exploration, and its combat is a real system with hundreds of weapons that behave differently. Beating a boss changes the world, new ores spawn, new enemies appear, whole biomes shift.

Re-Logic has released several final updates now, each larger than the last, and the 1.4 line left it with well over five hundred items and a hardmode progression that runs far longer than the pre-hardmode game most players remember. It supports eight-player co-op, costs very little, and runs on essentially anything.