Minecraft

for my first entry I will briefly talk about Minecraft.  If you haven't already heard about it you should definitely check this out.  Minecraft is free to play and there is also a pay to play version.  The idea is that the world is made of many different types of blocks.  These blocks can be destroyed, harvested, and used for building.  In the free version it is an open sandbox where you can create almost anything you can think of and show it off to people or play around in your little house.  Some people have even made entire cities or even replicas of things like the entire world of pokemon.  The pay to play version also has many other features like a survival multiplayer mode.

Heres a video of some people playing free version.
(EDIT: new video posted old one was taken down for some reason)