OpenTTD - An open-source clone of the classic game ...
Minetest - Minetest is a near-infinite-world block sandbox game and a game engine, inspired by InfiniMiner...
Micropolis - Micropolis is the open source version of SimCity Classic from Maxis, developed by Will Wright and Don Hopkins.
Roblox - Reimagining the way people come together.
Simutrans - Simutrans is an open-source transport simulator.
Minecraft - A block-building game that allows you to create and explore entire worlds from scratch.