Another big surprise to me -- Gnuplot is NOT free/open source software in the GNU sense: "Gnuplot is freeware in the sense that you don’t have to pay for it. However it is not freeware in the sense that you would be allowed to distribute a modified version of your gnuplot freely. Please read and accept the modification and redistribution terms in the Copyright file." (see http://www.gnuplot.info/faq/faq.html) I had to remove Gnuplot from SageMath because of their GPL-incompatible license.