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.
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.
HPGS is an HPGL/2 interpreter, which renders HPGL/2 and processes vector data through a Postscript-like API. It can render to EPS and PNG files. For rendering the scenery to pixel formats, it includes a rendering engine which draws vector graphics into pixel buffers. It also interprets inline PCL images.
UniConvertor is a universal vector graphics translator. It uses the sK1 engine to convert one format to another. There are import filters for CorelDraw (CDR and CMX), Adobe Illustrator (AI), Scalable Vector Graphics (SVG), and some other formats, and export filters for AI, SVG, WMF, and sK1's own format.