I am interested in making a MMO game but I am not sure where to start. I am looking for an open source game engine which is simple to use and allows me to concentrate on the game design and architecture. I have some basic C,C++,C# knowledge. After lots of searching in google I was going to start out with Ogre3D but soon realized that it is a rendering engine and does not include physics engine. I have not tried it yet since in many forums it says they don't have a good documentation. So is there any good open source game engine good for fast game developing ? Some key features I want include basic requirements like collision detection, object to object collision detection, physics etc.