Massive multiplayer online game

A massively multiplayer online game (MMOG or MMO) is an online game which is capable of supporting large numbers of players, typically from hundreds to thousands, simultaneously in the same instance (or world). MMOs usually feature a huge, persistent open world, although some games differ. These games can be found for most network-capable platforms, including the personal computer, video game console, or smartphones and other mobile devices.

MMOs can enable players to cooperate and compete with each other on a large scale, and sometimes to interact meaningfully with people around the world. They include a variety of gameplay types, representing many video game genres.

The most popular type of MMOG, and the subgenre that pioneered the category, is the massively multiplayer online role-playing game (MMORPG), which descended from university mainframe computer MUD and adventure games such as Rogue and Dungeon on the PDP-10. These games predate the commercial gaming industry and the Internet, but still featured persistent worlds and other elements of MMOGs still used today.

The first graphical MMOG, and a major milestone in the creation of the genre, was the multiplayer flight combat simulation game Air Warrior by Kesmai on the GEnie online service, which first appeared in 1986. Kesmai later added 3D graphics to the game, making it the first 3D MMO.

Commercial MMORPGs gained acceptance in the late 1980s and early 1990s. The genre was pioneered by the GemStone series on GEnie, also created by Kesmai, and Neverwinter Nights, the first such game to include graphics, which debuted on AOL in 1991.

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