BRL-CAD is a powerful constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, and image and signal-processing tools.
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.
DiaCanvas is a generalized version of the drawing canvas used by DIA. It extends some features used by DIA and adds new ones, while preserving as many of the original features as possible. This project is no longer actively maintained. It is suggested that you try DiaCanvas2 instead.
fsv, the 3D File System Visualizer, allows you to view a collection of directories and files as three-dimensional geometry. It represents all or part of a filesystem as a collection of blocks of varying sizes, each labeled with a filename, and arranged in a manner consistent with the original directory structure. fsv can visualize any arbitrarily large collection of files, limited only by memory and hardware constraints. Program features include an integrated 2D interface, intelligent camera handling, and extensive use of animation. fsv requires OpenGL.
GdkRgb is a rewrite of the image rendering subsystem of Gtk+. Advantages over plain Gtk+ 1.0.x include higher speed, very smooth and pretty dithered modes, and support for more displays and visuals. It is currently checked into development versions of Gtk+ (and used in the development tree of the Gimp), but is also packaged separately for application authors who want to maintain Gtk 1.0.x compatibility. The programming interface is quite simple.