Freecell

[xiphias]

You know that whole speculation about whether every starting position of the game Freecell (the addictive Solitare version that comes with Windows) is solvable? Well, I got curious about it and did a quick Google search, and found this.

It's not. Position number 11982 has apparently been proven unsolvable.

And some versions of Freecell include an ability to choose game number -1 and -2, which are two setups which are clearly unsolvable.

Neat, hunh?