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.
Jhead is a command line driven utility for extracting digital camera settings from the Exif format files used by many digital cameras. It handles the various confusing ways these can be expressed, and displays them as F-stop, shutter speed, etc. It is also able to reduce the size of digital camera JPEGs without loss of information, by deleting integral thumbnails that digital cameras put into the Exif header. If you need to add Exif support to a program, this is a simple program to cut and paste from. Many projects, including PHP, have reused code from this utility.
PLIB is a set of libraries to write games and other realtime interactive applications that are 100% portable across a wide range of hardware and operating systems. It's used by Majik3D, FlightGear, and others, and includes libraries for GUI widgets, sound replay, geometry, scene graph, joystick, and fonts/text.
QCad is a powerful but easy to use 2D CAD program for Linux, Windows, and Mac OS X. It uses DXF as its standard file format. While other CAD packages are often rather complicated to use, QCad tries to stay comfortable, and even an absolute beginner can create professional drawings with a minimum of effort.
Prima is an extensible Perl toolkit for multi-platform GUI development. Supported platforms include Linux, Windows NT/9x/2K, OS/2, and UNIX/X11 workstations (FreeBSD, IRIX, SunOS, Solaris, and others). The toolkit contains a rich set of standard widgets and has emphasis on 2D image processing tasks. A Perl program using Prima looks and behaves identically on X, Win32, and OS/2 PM.
SVGSlice is a simple tool which generates chopped up images from Inkscape SVG drawings. To figure out where to cut, SVGSlice can use Inkscape's built in guides (for simpler, grid-like cuts), or it can use a specially named "slices" layer that contains rectangles that mark areas to slice. Demo files showing both approaches are included.
view3dscene is a browser for VRML (1.0 and 2.0) and X3D, and a viewer for other 3D model formats (3DS, MD3, Wavefront OBJ, and Collada are handled). It supports viewing the scene in the "Examine" mode and walking in the virtual world with features such as collision detection and gravity. Rendering is done using OpenGL. Many advanced 3D graphic effects are available, like mirrors (flat and through cube environment mapping), shadows (shadow maps and shadow volumes), GLSL shaders and more. The program can also convert files from 3DS, MD3, Collada and other formats to X3D and pretty-print VRML and X3D files.