Why it's similar: Masterspace is pretty much just like Minecraft, except you have a space ship and there are an infinite number of planets to make your own. You can fly to any procedurally generated planet in Masterspace's galaxy, land on the voxel-based surface, and proceed to dig, craft, and customize the world as you see fit.
What makes it unique: The aforementioned space ship changes things up quite a bit. Not only can you fly around in space, but because you have space travel technology at your disposal, you won't be limited to tying two sticks and a rock together to make a pickaxe. Eventually, you'll be able to build laser guns, robots, and even customize your space ship.