Minetest - Minetest is a near-infinite-world block sandbox game and a game engine, inspired by InfiniMiner...
Infiniminer - Infiniminer is a multiplayer block mining game with several different player classes to choose from.
Roblox - Reimagining the way people come together.
Voxelands - The Fun-Focused Free Software Voxel World Game.
Terraria - Dig, Fight, Build! The very world is at your fingertips as you fight for survival, fortune, and glory.
Terasology - Terasology (started under the name Blockmania) is an open source project started by Benjamin...