Entropia Universe

Entropia Universe is a hugely popular and vividly detailed massive multiplayer (MMO) game! You can travel to different planets, trade in an in-game currency, tame a wild beast, and much more. Because Entropia Universe's in-game Project Entropia Dollars (PED) can be amassed within the game and exchanged for real-world money, various entrepreneurs have set up successful in-game businesses. Entropia Universe remains free-to-play though. You don't need to spend any money to sign up and play.