Online games are widely popular, especially MMORPGs (Massively multiplayer online role-playing games) like World of Warcraft, Everquest, Dungeons & Dragons, and Second Life. All of them simulate a virtual world with player interaction, as well as interactions with robots. In most such games, there are markets: players can buy objects, trade with each other, or participate in auctions.
One problem that can arise in such virtual environment is inflation: as players accumulate money, the amount of money in circulation may constantly increase, unless the "government" finds ways to reclaim some of that money. For example, some goods are required for continued play, and their price is preset and may fluctuate. Gaming companies hires economists to handle this (example) and prevent rampant inflation.
There are people studying the Economics withing these games (example). At Indiana University, there is even a research group dedicated to this. A new avenue for experimental economics?