I agree with you, the point I was trying to make was that since the project is open, using unity3d would be free, since everybody builds their own build. If at

I agree with you, the point I was trying to make was that since the project is open, using unity3d would be free, since everybody builds their own build. If at some point someone wanted to distribute and monetize the app, then yeah they'd have to pay the license fee. But in any case, the app is being written in c++ which I think is a harder but better language to write games in, mainly for performance reasons. I am not familiar with libRocket, but I am curious how well it will deal with a large scene graph, whether or not it support level of detail or culling, or if you have to handle that yourself.