Qt is a comprehensive, object-oriented development framework that enables development of high-performance, cross-platform rich-client and server-side applications. When you implement a program with Qt, you can run it on the X Window System (Unix/X11), Apple Mac OS X, and Microsoft Windows NT/9x/2000/XP by simply compiling the source code for the platform you want. Qt is the basis for the KDE desktop environment, and is also used in numerous commercial applications such as Google Earth, Skype for Linux, and Adobe Photoshop Elements.
GTK, which stands for the Gimp ToolKit, is a library for creating graphical user interfaces. It is designed to be small and efficient, but still flexible enough to allow the programmer freedom in the interfaces created. GTK provides some unique features over standard widget libraries.
U++ is a C++ cross-platform rapid application development suite focused on programmers' productivity without sacrificing runtime performance. Based on strictly deterministic design, it provides a viable alternative to garbage-collected platforms, even for business logic oriented problems.
Coin is an implementation of Open Inventor. Open Inventor is the de facto standard API for retained-mode 3D graphics programming. Open Inventor has a highly extensible design, and has been designed to allow for rapid development of highly interactive 3D graphics applications in the fields of CAD, engineering, scientific computing, simulation, VRML, and visualization.
OpenGUI is a high-level multi-platform, thread-safe C/C++ windowing and graphics library built upon a fast, low-level graphics kernel. It provides 2D drawing primitives and an event-driven windowing API for easy application development. The benefit of this library is speed, power, and a well-designed API with a narrow learning curve. It supports the BMP, JPG, TGA, PNG, TIFF, and PCX image file formats, color gradients, and TTF fonts. There is also basic XML file support and a smart persistence wrapper. OpenGUI supports the keyboard and mouse as event sources, the Linux framebuffer, SVGAlib, and XFree86/DGA2 (HW accelerated) as drawing backends, Mesa3D under Linux, and 8, 15, 16, and 32-bpp color modes.
Equalizer is middleware for creating and deploying parallel OpenGL-based applications. It enables applications to benefit from multiple graphics cards, processors, and computers to scale rendering performance, visual quality, and display size. An Equalizer-based application runs unmodified on any visualization system, from a simple workstation to large scale graphics clusters, multi-GPU workstations, and Virtual Reality installations.