A command-driven interactive graphing program. Gnuplot can plot two-dimensional functions and data points in many different styles (points, lines, error bars); and three-dimensional data points and surfaces in many different styles (contour plot, mesh). It supports complex arithmetic and user-defined functions and can label title, axes, and data points. It can output to several different graphics file formats and devices. Command line editing and history are supported and there is extensive on-line help.
Gnuplot is copyrighted, but freely distributable. It was written by Thomas Williams, Colin Kelley, Russell Lang, Dave Kotz, John Campbell, Gershon Elber, Alexander Woo and many others. Despite its name, gnuplot is not related to the GNU project or the FSF in any but the most peripheral sense. It was designed completely independently and is not covered by the General Public License. However, the FSF has decided to distribute gnuplot as part of the GNU system, because it is useful, redistributable software.