Second life is a 3D virtual environment which was entirely built and owned by its residents. Since opening to the public in 2003, it has grown massively and today is populated by a total of 2,954,687 people from around the world. Second Life is a 3D platform that can be used for: presenting, promoting, and selling content to a broad online audience; collaborating and communicating in real time between multiple participants; researching new concepts/products; and training and educating in virtual classrooms. An example screenshot from second life virtual world is shown below.
From the moment a user enters the virtual world, he/she must discover a large digital continent, teeming with people, entertainment, experiences and opportunity. As soon as the virtual world is explored then users must find a perfect parcel of land to build their house or business. It is also possible to be surrounded by the Creations of your fellow residents. Because residents retain the rights to their digital creations, they can buy, sell and trade with other residents. The Marketplace currently supports millions of US dollars in monthly transactions. This commerce is handled with the in-world currency, the Linden dollar, which can be converted to US dollars at several thriving online currency exchanges.More information:
http://secondlife.com/
http://blog.secondlife.com/