The very best thing about Open Simulator, is that it is free. With simply the cost of a co-located server (or dedicated home/office resources), and a little technical know-how, you can immerse yourself in a fully creative sandbox where your imagination is the only barrier. Review collected by and hosted on G2.com.
At least in my experience, there is no massively active community to explain setup and configuration in human language. If you are contimplating creating your own virtual world using OpenSim, you really kind of need to know your stuff on the tech side of things, however there have been some layer 2 solutions to make things a bit more friendly. Review collected by and hosted on G2.com.


