Roblox - more civilized version of Minecraft that takes place in a much safer world. Roblox' gameplay consists mostly of competing with other players in one of dozens of minigames, ranging from paintball to car races.
The Blockheads - protect your people and help them thrive in this vast, detailed 2D world.
Terraria - an adventure game. Explore the world, gather resources, craft items and fight enemies, with dynamic light and day-night cycle as a fancy bonus.
Growtopia - Minecraft's close that is completely about the creation aspect of the game - not only buildings and items, but also playgrounds, artwork, puzzles and even songs.