a free library providing windowing and widgets for graphics APIs / engines where such functionality is not natively available, or severely lacking. The library is object orientated, written in C++.
a real-time terrain rendering system supports asynchronous paging, dynamic terrain, and much more. It compiles under Irix, Linux, MacOS X and Windows (VC++ and cygwin).
a library for collision detection of three-dimensional objects undergoing rigid motion and deformation. SOLID is designed to be used in interactive 3D graphics applications, and is especially suited for collision detection of objects and worlds described
Simple DirectMedia Layer is a cross-platform multimedia library designed to provide low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D video framebuffer.
a font rendering library for OpenGL applications. It supports bitmap, textured, polygon, and outline glyph rendering and relies on FreeType for font loading.
a free application framework designed for "creative coding". OpenFrameworks is written in C++ and runs on Windows, Mac OS X, and Linux. It is developed and maintained by Zachary Lieberman and Theo Watson.
C++ libraries for advanced machine and robot control, supporting 4 C++ libraries: the Real-Time Toolkit, the Kinematics and Dynamics Library, the Bayesian Filtering Library and the Orocos Component Library.
a C++ Web development framework (not CMS). It differs from most of other Web development frameworks like Python Django, Java Servlets, or C++ Wt because it is designed and tuned to handle extremely high loads, and it is aimed at development of Web sites rather then "GUI-like" Web applications.