Ultima Online began with a single world, with specific expansion packs adding additional territory and new worlds. Partially designed as a social and economic experiment, the game designers had to account for widespread player interaction as well as deal with the tradition of players feeling as if they were the center of attention, as had been the case in single-player games. Ultima Online continued the tradition of previous Ultima games in many ways, but due to advancing technology and the simple fact that it was Origin's first persistent online game, many new game mechanics appeared. The release of Ultima Online: Kingdom Reborn in 2007 brought a new game engine with upgraded visuals. Since its release, it has added eight expansion packs, a booster pack, and dozens of free content updates. Set in the Ultima universe, it is known for its extensive player versus player combat system. Ultima Online ( UO) is a fantasy massively multiplayer online role-playing game (MMORPG) released on Septem by Origin Systems.