What are all good GUI & plotting package options for Maxima?

> Gnuplot is not GPL compatible.  This limits our freedom
> with this one.
> I'd like to hear what are other quality GPL
> compatible plotting packages out there.

Though I'd also be interested to know what other packages are out there
(and their advantages and disadvantages), let's not write off gnuplot
for license reasons just yet.

As long as gnuplot and Maxima maintain an arm's-length relationship,
communicating through well-defined protocols in separate processes, and
not commingling source files -- that is, as long as they remain
"separate works" in the GPL's legalese -- I do not think that Maxima's
GPL prevents us legally from using gnuplot.  Indeed, if I'm not
mistaken, Octave (which is GPL'ed) uses gnuplot.

The next question is whether gnuplot's license is acceptable to us --
that is, whether it is "free enough".  The main restriction it imposes
is that source redistribution must be done with diffs, not modified
files.  Given that we maintain source with CVS, we essentially get this
for free.

So what's the problem?

       -s