Second Life is a massively-multiplayer world developed by Linden Labs. Unlike many other MMGs there is no particular aim, rather the intent is to live in the world and add to it. Thus importantly it is the game’s participants that create and develop the universe they inhabit (its creators explicitly invoke the Metaverse of Neal Stephenson’s Snowcrash as a model).
MMG (massively multiplayer games) solve the central problem that current computer technology faces in creating interesting games: namely no decent AI. Without AI all the interesting parts of a ‘world’ have to lovingly crafted by hand. Thus while we can draw some lots of pretty stuff we are a) we are severely limited in the size and variety of the world’s artifacts and geography b) /very/ limited in the other entities that we can interact with.
Standard MMRPGs such as EverQuest address problem (b) in a limited way by using the games participants to populate their world. However one is still restricted by the fact that such participants must remain within the contours of the plot and the surrounding reality as well as by the need to provide backup computer generated entities (be it for the dull occupations in this online world or until the strong law of large numbers kicks in). Moreover this type of games fails to leverage the games own /participants/ to help create/extend the world (much). A game such as Second Life (there are several others that have gone down that route) takes this logical next step and allows both (a) and (b) to be addressed. The final step would be to integrate some kind of incentive mechanism though it should be noted that Second Life appears to demonstrate that is not strictly necessary to get the participants to contribute.