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.
GL2PS is a C library providing high quality vector output for any OpenGL application. It uses sorting algorithms capable of handling intersecting and stretched polygons, as well as non manifold objects. It provides advanced smooth shading and text rendering, culling of invisible primitives, mixed vector/bitmap output, and much more. It can currently create PostScript (PS), Encapsulated PostScript (EPS), Portable Document Format (PDF), and Scalable Vector Graphics (SVG) files, as well as LaTeX files for the text fragments.
KVEC is a command line tool that allows you to convert raster graphics to vector graphics. KVEC is designed for 32 bit operating systems and runs on Win32, OS/2, HP-UX, NEXTSTEP, Linux, IRIX, AIX 4.x, Macintosh and BeOS. Docs are available in English and German. The shareware version is available for 30 day trial.
Kabeja is a Java library for parsing CAD data (i.e. Autodesk's DXF format) and converting to SVG (dxf2svg). You can use Kabeja from the command line or embed it into your application. It includes a plain DXF2SVGViewer and integration into the Cocoon XML Web development framework and the Inkscape SVG editor.