RuneScape

the following was a description taken from Runescape.com's beginner's world page.

 Description: Anyone can pick up and play RuneScape. RuneScape doesn’t require any downloads at all and can be accessed almost instantly via the web’s most popular browsers. RuneScape is consistently hailed as one of the most immersive free MMOs available on the web – so much so that it entered the Guinness Book of World Records in 2008 as the world’s most popular free MMORPG!

With over 175 million registered users, players can explore the realms and cities within Gielinor of their own free will, doing all they can to rid the land of evil forces and express themselves through their actions – whether helpful, mischievous or downright despicable...