SporE was demoed at GDC, is covered e.g. in http://www.gamingsteve.com/
WikiWorlds? at http://virtualworlds.wikia.com/wiki/Main_Page aims to "create virtual worlds under a free content license".
DarkFall? http://forums.darkfallonline.com/archive/index.php/t-17872.html (has a CharacteR? called RogdorDeFault)