OpenSimulator

[elspudo]

Web 3D equivalent of Apache http://opensimulator.org/

[jcorbett]

We're currently using Opensim for a primary school project in association with the Communicating Europe Day. Our server is being hosted by ReactionGrid which I'd highly recommend to anyone who wants to explore Opensim. These guys are so much more than hosts - they have weekly 'office hours' in-world, offer free in-world tutorials and classes, respond quickly to twitter questions and have a terrific community spirit.