Calc III is taught here with Mathematica, and a colleague here
happily determined that everything necessary for our Calc III could
be done by Maxima as well.
(http://vh224401.truman.edu/~dbindner/calc3/)
(His joke: "Today is the car of the cdr of your life.")
However, to get contour plots, a function had to be graphed in
gnuplot and then the right gnuplot commands had to be given.
I've seen other questions about contour plots, and it seems to be
something wanted but not (really) available.
It'd be pretty easy to add an option to mgnuplot to allow it to draw
contour plots. The problem is that it would be specific to gnuplot,
but that's better than not having it at all.
Another nice feature that I think would be nice would be the
ability to draw over already drawn graphs. This would be easy to do,
but again it'd be gnuplot specific. (Maybe it'd be easy to do in
general, I don't know.)
Is there any interest in having gnuplot specific drawing commands?
Jay