I've recently gotten addicted to HSX, or Hollywood Stock Exchange, a web-based game that centers around a stock-market style mechanism for wagering on the success or failure of movies at the box office.  It's all fake money, of course, but I find it a very potent combination of my love of movies and love of stat crunching and general game-theory analysis.  While I'm not really sure the HSX guys would necessarily refer to it as a "game", to me it is very clearly a multiplayer game, one that is very cleverly leveraged into real world events.

"Game" is often viewed as a dismissive or derogatory term, which of course I do not mean.  Actually I think the predictive powers of a system like this is a fascinating example of how game mechanics and game theory can be leveraged to harness the predictive powers of large groups of people behaving in statistically motivated ways (c.f. The Wisdom of Crowds).  A study of how the predictions of HSX correlate to actual results would certainly be interesting to see, and gives "games" like this a kind of utility that is quite unique.

It would be fascinating to see something like this set up for game releases, though the shoddy state of game sales tracking would make it all but impossible.  I could imagine it being used as a mechanism for predicting popularity of key brands and franchises however.  It is a perfect example of how very simple rules can generate quite complex behavior -- a very elegant solution for the Gordion Knot of how to model human beings.