Guild Wars is an episodic series of online 3D fantasy role-playing games developed by ArenaNet and published by NCsoft. Although often defined as an MMORPG the developers define it as a CORPG due to significant differences from the MMORPG genre. It provides two main modes of gameplay—a cooperative role-playing component and a competitive player vs. player (PvP) component—both of which are hosted on ArenaNet's servers. Three stand-alone episodes and one expansion pack were released in the series from April 2005 to August 2007. The games depict the history of the fictional fantasy world of Tyria; each campaign focuses on events in disjoint sections of the world at roughly the same time. A player creates an avatar to play through the cooperative storyline of a campaign, taking on the role of a hero who must save Tyria from episode-specific antagonists. Players can group with other players and non-player characters, known as henchmen and heroes, to perform missions and quests found throughout the game-world. PvP combat is consensual, team based, and limited to areas designed for such combat. Players are allowed to create characters at maximum level and the best equipment specifically for PvP play, which is unusual for MMORPGs. ArenaNet hosts official Guild Wars tournaments where the most successful players and guilds may compete for the chance to play live at gaming conventions and win prizes up to US$100,000. Guild Wars differs from other MMORPGs in its lack of subscription fees (purchasing an episode allows a user to play it online without limit, though he or she may encounter some areas or items which cannot be obtained without purchasing other episodes) and relatively low level caps. After reaching the level cap, players differentiate their characters by which skills they equip to bring into battle; new skills can be learned by exploring and completing quests. Only eight of a player's learned skills can be equipped at any one time, the ongoing challenge being to select skills that synergize well in the next combat environment. The games in the Guild Wars series were critically well received and won many editor's choice awards, as well as awards such as Best Value, Best Massively Multiplayer Online Role-Playing Game (MMORPG), and Best Game. Guild Wars was noted for being one of the few commercially developed games in the MMORPG genre to offer online play without subscription fees, its instanced approach to MMORPG play, and the quality of the graphics and play for computers with low specifications. In April 2009, NCSoft announced that 6 million units of games in the Guild Wars series had been sold. The sequel, Guild Wars 2, was announced in March 2007. It will have updated graphics and gameplay mechanics, and will continue the original Guild Wars tradition of no subscription fees. No release date has been announced.