Entropia Universe (Steam)

Entropia Universe is an advanced 3D online virtual environment with a developed planetary system and one universal Real Cash Economy system. Each planet offers a wide variety of exciting entertainment. You can travel between the planets through space and socialize with people from all over the world. It does not cost anything to join and there are no subscription fees. The Entropia Universe economy is built on an advanced micro-payment system, giving you as a participant a great freedom-of-choice.