OpenSimulator

• What is OpenSimulator

For those that know about Second Life, well this is exactly what OpenSimulator is.

OpenSimulator is a 3D Application Server. It can be used to create a 3D Virtual World (ala Second Life(tm)), and includes facilities for creating custom avatars, chatting with others in the environment, building 3D content in world, and creating complex 3D applications in world. OpenSimulator can also be extended via loadable modules or web service interfaces to build more custom 3D Applications. OpenSimulator is released under a BSD License, making it both open source, and commercially friendly to embed in products.

So to put it simple OpenSimulator is one big multiplayer SIMS with no limitations what so ever.