The granddaddy of open-source MMORPGs: PlaneShift is a Role Playing Game (with capital letters) immersed into a 3D virtual fantasy world, completely made and maintained by volunteers! Passionate RPG gamers gathered to create an open and freely available game. It is fully open to play, e.g. there are no limitations in skills, ranks, abilities, items you can gain with your free account.
PlaneShift is based on the GPL CrystalSpace engine, but all artworks and other media are only licensed for free use in this game.