Minetest - Minetest is a near-infinite-world block sandbox game and a game engine, inspired by InfiniMiner...
Amulet Map Editor - The Amulet Map Editor is a new and innovative Minecraft map editor made by the Amulet Team, a team formed by the contributors that brought you MCEdit-Unified
Roblox - Reimagining the way people come together.
WorldEdit - Minecraft MOD - WorldEdit is an easy-to-use in-game Minecraft map editor. Through a combination of commands and "brushes," you can sculpt your world or simply perform numerous terraforming tasks.
Terraria - Dig, Fight, Build! The very world is at your fingertips as you fight for survival, fortune, and glory.
GriefPrevention - Minecraft Server Plugin - Stop responding to grief and prevent it instead. Grief Prevention will solve your grief problems without a roster of trained administrators, without 10 different anti-grief plugins, and without disabling any standard game features.