The OpenGL Object-Orientated Windowing Environment provides a C++ OO basis from which to develop OpenGL projects, giving you all the usual widgets (buttons etc) and a windowing framework. Good for cross-platform development.
A self-sufficient java framework for numerical solution of ODEs (diff eqs) and visualization. Samples are aeronautics/astronautics/physics/rocketry themed. Focus on clean design, modularity, reusability and documentation. Educational project.