Ryzom

Immerse yourself in a massive sandbox world. In Ryzom or The Saga of Ryzom, is an MMORPG in which, instead of classes, it allows you, the player, to form your own spells or attacks. The setting of the game is the layered planet of Atys which, unlike other planets, is actually a tree. Fight against monsters and challenge other players in PvP mode, or even better, build your own using the scenario editor, upload it, and play on your own terms.