RuneScape
RuneScape is a massively-multiplayer online game (MMOG), set in a fantasy world of warring races, ravaged landscapes and sinister powers. Having chosen an adventurer, players are free to find their role within it: to live by the sword and face hundreds of enemies, to further the storyline in RuneScape's quests, or to train in any of a number of skills.
RuneScape can be played directly in your browser, requiring no installation. It is also free to play, offering everyone the chance to explore the involving story and vast game area without paying a single gold piece!