Gri graphical language
Gri is a GPL-licensed language for scientific graphics programming. The word "language" is important: Gri is command-driven, not point/click.
Some users consider Gri similar to LaTeX, since both provide extensive power as a reward for tolerating a learning curve.
Gri can make x-y graphs, contour graphs, and image graphs, in PostScript and (someday) SVG formats. Control is provided over all aspects of drawing, e.g. line widths, colors, and fonts. A limited TeX-like syntax provides common mathematical symbols.
Folks who write thousand-line Gri scripts usually start with something as simple as the following, which produces an auto-scaled graph.
open file.dat read columns x y draw curve