PLplot is a library of C functions that are useful for making scientific
plots from a program written in C, C++, or Fortran. The PLplot library
can be used to create standard x-y plots, semilog plots, log-log plots,
contour plots, 3D plots, mesh plots, bar charts and pie charts. Multiple
graphs (of the same or different sizes) 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. There are almost 1000 characters in the extended
character set. This includes four different fonts, the Greek alphabet and
a host of mathematical, musical, and other symbols. The fonts can be
scaled to any desired size. A variety of output devices are supported and
new devices can be easily added by writing a small number of device
dependent routines.
WWW: http://plplot.sourceforge.net/