D'Enfent Engine is a library that contains high-level classes to access OpenGL functions. It contains classes that may be very useful in game development: GUI components, sprite classes, and classes to handle mouse/keyboard events. It has a full API reference, as well as lessons to help you start working with the library.
Angel is a 2D game prototyping engine based on OpenGL and C++. It was originally made by a group of employees at Electronic Arts Los Angeles for use in a GameJam they were planning for April of 2008. Angel provides many useful functions for prototyping gameplay, including simple physics, particles, text rendering, sound, input mappings, config files, pathfinding, and Python scripting.
MV3D is a virtual world and multi-player game framework for use with Python. It was designed with scalability in mind and is able to distribute a world across as many servers as needed while dynamically balancing the load. The simulation framework is not specifically slanted towards any one genre of online game or virtual world, and can just as easily be used for a space game as a fantasy setting. Objects on an MV3D server can be simulated using the ODE physics engine for realistic interactions. A single server is able to host thousands of of simulated objects. The client works with both the Ogre3D and Panda3D renderers.
Visualization Library is C++ middleware for high-performance 2D and 3D graphics applications based on the industry standard OpenGL 1.x-4.x, designed to develop portable applications for the Windows, Linux and Mac OS X operating systems. It supports advanced features like OpenGL Shading Language, Volume Rendering, Isosurface extraction, Frame Buffer Objects, Multiple Render Targets, Vertex and Pixel Buffer Objects, KdTree/AABB frustum culling, a multilingual Unicode-based text engine, advanced texturing, DDS cubemaps, mipmaps, compressed textures, and much more. Visualization Library can be especially useful in 3D/2D scientific visualization, virtual reality, augmented reality, visual simulation, data visualization, presentations, multimedia applications, special effects, and 3D/2D games.