[jeznav]

Although Unity is not 100% publicly open-source without requesting for their source code license, they have released a bunch of their source code to the public.

http://blogs.unity3d.com/2014/11/26/4-6-is-released-with-sou...

https://github.com/Unity-Technologies

https://bitbucket.org/Unity-Technologies/

Asset/Cache Server: http://unity3d.com/unity/collaboration/

Built-in Shaders: http://unity3d.com/download_unity/builtin_shaders.zip