A massively multiplayer online game (also called MMO and MMOG) is a Multiplayer video game which is capable of supporting large numbers of players simultaneously. By necessity, they are played on the internet. Many games have at least one persistent world, however others just have large numbers of players competing at once in one form or another without any lasting effect to the world at all. These games can be found for most network-capable platforms, including the personal computer, video game console, or smartphones and other mobile devices. MMOGs 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 debuts of The Realm Online, Meridian 59 (the first 3D MMORPG), Ultima Online, Underlight and EverQuest in the late 1990s popularized the MMORPG genre. The growth in technology meant that where Neverwinter Nights in 1991 had been limited to 50 simultaneous players (a number that grew to 500 by 1995), by the year 2000 a multitude of MMORPGs were each serving thousands of simultaneous players and led the way for games such as World of Warcraft and EVE Online
Despite the genre's focus on multiplayer gaming, AI-controlled characters are still common. NPCs and mobs who give out quests or serve as opponents are typical in MMORPGs. AI-controlled characters are not as common in action-based MMOGs. The popularity of MMOGs was mostly restricted to the computer game market until the sixth-generation consoles, with the launch ofPhantasy Star Online on Dreamcast and the emergence and growth of online service Xbox Live. There have been a number of console MMOGs, including EverQuest Online Adventures (PlayStation 2), and the multiconsole Final Fantasy XI. On PCs, the MMOG market has always been dominated by successful fantasy MMORPGs. MMOGs emerged from the hard-core gamer community to the mainstream strongly in December 2003 with an analysis in the Financial Times measuring the value of the virtual property in the then-largest MMOG, Everquest, to result in a per-capita GDP of 2,266 dollars which would have placed the virtual world of Everquest as the 77th wealthiest nation, on par with Croatia, Ecuador, Tunisia or Vietnam. Happy Farm is the most popular MMOG with 228 million active users, and 23 million daily users (daily active users logging onto the game with a 24-hour period).