Others like Second Life, Nodiatis and Star Trek Online have also become popular.
But before that there were other games such as Ultima Online, and even text based game platforms like MUDs (Multi-User Dungeons), which also have a real-time virtual reality element.
Elysarian Kingdoms Graphics: No Download: No Needs to be bought: No Browser-based MMORPG set in a fantasy world filled with a plethora of different races. Materia Magica Graphics: No Download: No Needs to be bought: No Text-based online RPG where you encounter such classic monsters as trolls, goblins, giants and dragons.
Note that some features like marriages have not been implemented yet. The best part, however, is the ability to play as an ogre!
Throw in the online playability of and you have the recipe for on of the greatest selling PC games of all-time.