It's illegal to print money - even if you don't disguise it as government currency. That's why casino's can't accept each others chips - before you know it they would be competing with the Federal Reserve.
How about Blogshares? On one level it's a casual web browser game. You can buy and sell shares of blogs as if they were companies. The number of links from other blogs and recent blogshare buying and selling both figure into the price. One way to make an (imaginary) profit is to figure out which blogs will be growing in the near future - before other players do. It's a casual web browser game though, and you can make a profit easier than that. Buy a big block of almost any blog 'stock', then make smaller purchases over time. Then sell it all. Unless you pick a blog with a high P.E. (basically an overpriced blog, since there's no real earnings, just a measure of the number of links) you'll make a profit, since it goes up each time you buy. After you sell it all as a block, better pick a different blog stock - it didn't go all the way down.
This may sound easy, but it can be compulsive - and plenty of browser based games are no more complex than that and still get many players. Anyhow, there's much more to the game than that - if you want to be one of the top players. You can earn chips and karma by voting to characterize blogs by 'industry' - that is, political blog, science blog, business blog, craft blog, education blog ect. There is more than one level (liberal and conservative political blogs). You can earn sigma and chips by looking for inactive and deleted blogs. The end result is that if you want a list of active liberal (or conservative) blogs, blogshares is one of the best places to go. Unlike other blog directories, they don't rely on bloggers to register their own blogs - they use spiders, and players have incentives to find new blogs - and categorize old ones. Bloggers also have no incentive to delete their own inactive blog from a directory when they lose interest in it.
Blogshares cash (B$), chips, karma, and sigma all cost the game owners nothing. The game seems to be a labor of love, supported in part by donations. For a few dollars a month you get unlimited trading and other advantages. Oh yes, they also sell advertising for cash to google and others. Even if they need volunteers to keep going, there's potential here - getting people to do real work for imaginary money. This seems to go one better for the Mechanical Turk model of crowdsourcing.
The blog index without the game can be found at QuackTrack.