Minecraft is a sandbox construction game created by Markus Persson and is currently in pre release alpha. Minecraft development started around the 10th of May 2009, pre-orders for the full game started being accepted on the 13th of June.
The game involves players creating and destroying various types of blocks in a three dimensional environment. The player takes an avatar that can destroy or create blocks, forming fantastic structures, creations and artwork across the various multiplayer servers in multiple game modes. This was taken from Minecraft wiki.
This game is seriously so much fun and so addicting. You can create so many awesome things.