mathplot is a GUI frontend for interactive graphing of functions.
mathplot2ps is a batch program to generate PostScript output.

You can have both equations (y=f(x) or f(x,y)=g(x)) and inequations.
For inequations, mathplot hatches the intersection. For example, with
y>0, y<x and x<2 it hatches the solution which is a triangle. You can
name a point, anywhere or on a function. You can ask for the tangent
of a function. As it uses a symbolic library, you can enter functions
like "x+1/y=2". Can find root (zeros), extrema (even symbolically,
sometimes) and intersection of two functions. mathplot exports in
PostScript so that you can print easily, and with the reference mark
(O, i, j). You can save and load files. mathplot2ps can transform
these files into PostScript.
It's written in OCaml using the Tk toolkit for the GUI frontend.