The simExchange is a web-based prediction market in which players use virtual money to buy and sell stocks and futures contracts in upcoming video game properties. (to quote Wiki).
I joined them quite along time ago as I was attracted to the concept of using knowledge of news and gaming trends to 'predict' the sales levels of hardware and software over time. I had played fantasy stock markets and HollyWood Stock Exchange and felt this would be something I would enjoy.
In the beginning it seemed that most of the participants at the site had a genuine interest in the lofty goals of the site but as time has gone on and the simexchange changed from 'experiment' to 'let's monetize this' it strayed from its goals. (that is my pov).