Terasology!

Minetest is a near-infinite-world block sandbox game and a game engine, inspired by InfiniMiner, Minecraft, and the like.

Mythruna is a game under construction combining extensive world building, crafting, and sandbox elements with just a touch of role-playing. When completed, Mythruna will be a unique gaming experience.

The Fun-Focused Free Software Voxel World Game.

A completely clean-room implementation of Minecraft beta 1.7.3 (circa September 2011). No decompiled code has been used in the development of this software. This is an implementation - not a clone. TrueCraft is compatible with Minecraft beta 1.7.3 clients and servers.

ROBLOX is an online virtual playground and workshop - where kids of all ages can safely interact, create, have fun, and learn.

Freeminer is a Minecraft-inspired sandbox game.

In a galaxy of procedural worlds made entirely from LEGO bricks, will you...

You are marooned on the shores of an infinite blocky world. Explore, mine resources, craft tools and weapons, hunt and make traps. Build a shelter to survive nights and share your worlds online. Possibilities are infinite in this sandbox survival and construction game.

Creativerse is a sandbox adventure game set in a beautiful yet treacherous world shrouded in mystery. Adventure solo or bring your friends, unearth secrets, and tame the land together!

Build your dream island in a 3D, blocky world! Play with friends in real-time!

MineDroid is a viewer / concept design for Minecraft that supports using your own 1.3 beta levels, temporarily building and destroying blocks, sensor steering, crouch jump, ghost mode / fly mode. more features to come, you can get the source and help out too

Manic Digger is an open-source implementation of block-building games, like the famous game Minecraft.Manic Digger aims to be a generic platform ontop of which you can create your own game-types and scenarios. Through server-side scripting, almost any type of block-building game should be possible.

Kidblock is: Building, exploring, world sharing, multiplayer, mobs, rocket launchers, lasers, TNT, swords, crafting, mining, farming, protecting, gameplay recording and much more!

Infiniminer is a multiplayer block mining game with several different player classes to choose from.The object of the game is to collect loot while trying to keep the other team from accumulating loot.