Asymptote (Vector Graphics Language)
Asymptote is a powerful graphics language designed for creating mathematical diagrams and figures. It can output images in either eps or pdf format, and is compatible with the standard mathematics typesetting language, LaTeX. It was inspired by MetaPost, but has cleaner syntax. As opposed to being just a graphics program, it is a complete programming language.
Here is an example of an image that can be produced using Asymptote:
In a sense, Asymptote is the ruler and compass of typesetting.