Gnuplot is a command-driven interactive function plotting program.

Plots any number of functions, built up of C operators, C library
functions, and some things C doesn't have like **, sgn(), etc.  Also
support for plotting data files, to compare actual data to
theoretical curves.

User-defined X and Y ranges (optional auto-ranging), smart axes
scaling, smart tic marks.

Labelling of X and Y axes.

User-defined constants and functions.

Support through a generalized graphics driver for AED 512, AED 767,
BBN BitGraph, Commodore Amiga, Roland DXY800A, EEPIC, TeXDraw, EmTeX,
Epson 60dpi printers, Epson LX-800, Fig, HP2623, HP2648, HP75xx, HPGL,
HP LaserJet II, Imagen, Iris 4D, MS-DOS Kermit, Kyocera laser printer,
LaTeX, NEC CP6 pinwriter, PostScript, QMS QUIC, ReGis (VT125 and
VT2xx), SCO Xenix CGI, Selanar, Star color printer, Tandy DMP-130
printer, Tek 401x, Tek 410x, Vectrix 384, VT like Tektronix emulator,
Unix PC (ATT 3b1 or ATT 7300), unixplot, and X11.  The PC version
compiled by Microsoft C supports IBM CGA, EGA, VGA, Hercules, ATT
6300, and Corona 325 graphics.  The PC version compiled by Borland C++
sup- ports IBM CGA, EGA, MCGA, VGA, Hercules and ATT 6300 graphics.
Other devices can be added simply, but will require recompiling.

Shell escapes and command line substitution.

Output redirection.

WWW: http://www.gnuplot.org/