The G3D Innovation Engine is an open source C++ 3D game engine with a staggering amount of functionality, while also being incredibly education friendly. There is even a book that goes hand in hand with the engine for teaching advanced graphics programming. Whether you are looking for a low level cross platform (Mac, Windows, Linux) 3D framework, a full blown (minus physics) game engine, or just for sample code to learn 3D graphics programming, G3D may be the perfect choice for you.
You can learn more at:
The companion to this engine is available at:
The creator/maintainer of the engine is: