PLplot is a library of C functions that are useful
for making scientific plots from programs written
in a wide variety of languages. It can be used to
create standard x-y plots, semi-log plots, log-log
plots, contour plots, 3D plots, shade (gray-scale
and color) plots, mesh plots, bar charts, and pie
charts. Multiple graphs may be placed on a single
page with multiple lines in each graph. Different
line styles, widths, and colors are supported. A
virtually infinite number of distinct area fill
patterns may be used. A variety of output devices
and file formats are supported.