Anarchy Online is a MMORPG published and developed by Funcom. Released in the summer of 2001, the game was first in the genre to include a science-fiction setting, dynamic quests, free trials, and in-game advertising. By the end of 2002, Anarchy Online had recovered from the launch woes and even won the MMO of the Year award from PC Gamer. The company went on to create expansions, including the Shadowlands expansion in 2003 that earned several Editor's Choice awards.
The game's ongoing story revolves around the fictional desert planet Rubi-Ka, the source of a valuable mineral known as "notum". Fighting for military and political power on Rubi-Ka are the Omni-Tek corporation (owners of the planet's thousand-year lease), the separatist Clans, terrorist groups, aliens, and ancient civilizations. The narrative was developed to be played out as a series of virtual role-play events over the course of four years, influenced by the actions of those playing the game. Players assume the roles of new colonists to Rubi-Ka, represented by a persistent 3D virtual world. With no specific objective to win the game, they improve their characters' skill and status over time. This free-form progression leads to social networking, cooperation, and conflict with other players.
After ten years, Anarchy Online has become one of the oldest surviving games in the genre. Its "Free Play" program, called as "froobs" in the community, started in 2004, and allows new players indefinite access to the original game in return for viewing in-game advertisements.
I used Wikipedia article as base, and you can see it for more information as well. Or you might want to check out some more Anarchy Online specific sites, such as AO Universe, Anarchy Online on Wikia or Official forums.