Entropia Universe, a massively multiplayer online game set in a science fiction universe full of spaceships and fantastic curiosities. It is a game where players can choose from a wide variety of professions to occupy themselves with which in turn builds a diverse and functioning economy.

Entropia universe is worth discussing because of one very small aspect that makes a very big difference. The currency in the Entropia universe can be traded back and forth for real-world money, meaning it is effectively a video game that you play using real-world currency. And it was also an entirely exchangeable digital currency that existed 7 whole years before bitcoin came onto the scene.