It's an unreleased game that is similar to minecraft but, and I can't stress this enough, is NOT A RIPOFF. It is it's own thing, and when it releases is, it will have some BIG differences. For example:
-it will have an official storyline, not just a boss fight
-beating the game will take MUCH longer than minecraft
-the biome system will be more advanced and realistic
-modding will be easier
-it won't have multiple dimensions
-it has more mobs
-it has more specialized building material, but less building versatility