Terraria - Dig, Fight, Build! The very world is at your fingertips as you fight for survival, fortune, and glory.
Blockland - Blockland is a non-competitive multiplayer sandbox-style construction game. It's kind of like playing with legos on the internet.
Vintage Story - Survival voxel sandbox game inspired by Minecraft, Terrafirmacraft, Don't Starve and Dwarf fortress
NERF Arena Blast - The website linked is not real page, just moddb page.
Minetest - Minetest is a near-infinite-world block sandbox game and a game engine, inspired by InfiniMiner...
Blocksworld Wool - Download mods for Blocksworld!