I've collected a table of existing open source plotting packages I've found, with emphasis on 3d plotting and plotting libraries. Most of these libraries are hosted on SourceForge. I've only put programs that I was able to compile and run on my system.
|gnuplot||http://gnuplot.sourceforge.net/||yes||yes||yes||?||yes||yes?||?||a long-standing open-source plotting package. it is used as the plotter for octave|
|PLplot||http://plplot.sourceforge.net/||yes||yes||?||?||yes||yes||C, X||simple and fast|
|MayaVi||http://mayavi.sourceforge.net/||yes||?||yes||?||yes||no?||VTK||very pretty plus lots of capabilities. can't be used as a library [?]|
|MeTa->phi||http://metaphi.sourceforge.net/||yes||?||no?||yes||yes||?||openGL, SDL||very pretty and seemingly fast|
|g2 graphical library||http://g2.sourceforge.net/||yes||yes||yes||no?||no||yes||C||2d plotting library|
|xplot||http://mathdev.sourceforge.net/||yes||yes||yes||?||yes||?||openGL||buggy behavior on first investigation. no 2d?|
|GLPlot||http://glplot.sourceforge.net/||yes||no||no||no||yes?||yes||multiple||Many dependencies...wouldn't compile on my system! Gnome based|