The Universal... is an online game for PC. Explore the galaxy, play on planets or make your own world with your own game design. Various game types are available - including uniquely complex social economies - and you can play it all for free. If you're the creative type you'll find extensive in-game tools and a powerful scripting engine to let you create new game ideas. Or you can just mess around and blow each other into ostriches. It's all cool, whatever.
A picture from Biplaneworld following the first-pass implementation of an almost 21st century landscape shader.