Second Life

http://www.secondlife.com

What is Second Life and how does it impact on education?
According to the website...

Second Life provides a unique and flexible environment for educators interested in distance learning, computer supported cooperative work, simulation, new media studies, and corporate training.
Second Life provides an opportunity to use simulation in a safe environment to enhance experiential learning, allowing individuals to practice skills, try new ideas, and learn from their mistakes. The ability to prepare for similar real-world experiences by using Second Life as a simulation has unlimited potential!
Students and Educators can work together in Second Life from anywhere in the world as part of a globally networked virtual classroom environment. Using Second Life as a supplement to traditional classroom environments also provides new opportunities for enriching an existing curriculum. Many universities and educational institutions are already using Second Life, and you can find an updated list of them here.
There are many options for Educators looking to explore and create learning spaces in Second Life. Here is a comprehensive list of resources to help you get started.