This project is not currently being supported but feel free to use it as an example.
delta3d is a robust simulation platform built using open standards and open source software. It features full toolchain development supporting a wide variety of free and commercial software.
MV3D is an open source virtual world simulation framework written in Python. It was designed with scalability in mind and aims to be able to distribute a world across as many servers as needed while dynamically balancing the load.