Gnuplot was my first experience dealing with an open source project when I was starting my career. I went to their IRC channel and asked something related to the GNU project. I was immediately scolded: "Gnuplot is not a GNU project!!" :D
The license it's essentially a BSD with the (absurd) restriction that you can't distribute the "complete modified source code", whatever that means, but only patches. I wonder what's the motivation.
Distribution of software was different then.