I just ran across Real Engine looking for Architectural Visualization software (note that Twinmotion is free until Nov!) This is an amazing space which I imagine will explode in variety of application, especially once VR goes mainstream.

Are there any open source alternatives which even come close?

I wonder if I would attract attention if I were to upload a rendering of Saudi oil infrastructure for drone simulation. ;)

Can we use this thing as a simulation for shooting drones out of the sky? This could be an interesting massively multiplayer research project creating an arms race between attackers and defenders.