ExtZy is a prediction market game created by Z/Yen, which makes a market out of web-pages. Players can buy shares in those sites that they think will grow in popularity, and then trade their dividends in for real prizes. 

Take a look at the "Market", read the "One-Minute Guide to ExtZy", read the "Rules" of the game, build your "Portfolio" and set your eye on the top "Prizes".  While you're logged in, add your thoughts and questions to the "Forums", dig into the "Help" files for more background on buying and selling, and "Contact Us" with suggestions, feedback, and bug-reports!