From the creator of Minecraft, this is Minicraft. It's a top-down 2D game, like the old Zelda titles, that plays like a simplified version of Minecraft itself.
You can download the file here, or play the game online. Minicraft was created in 48 hours for a Ludum Dare competition with the theme 'Alone'. Like its big brother, in Minicraft you are free to roam around wherever you want, looking for resources and fending off monsters.
Not quite Minecraft...
While Minicraft is quite charming, and gives you the same desire to explore that Minecraft does, it's a pretty shallow game. That shouldn't be a surprise as it was made in a really short time, but Minicraft does feel like it deserves more development to be a finished game. There isn't really a lot to do, so once you've explored a bit and killed a few monsters… that seems to be all!