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
During my teenage years when I first started C++ (thank you Accelerated C++), I went to the ##c++ channel on Freenode and was immediately flamed for my "weird" nick, to the point that the people didn't bother to answer my question but instead went after me personally, just because I had picked a nick based on leet speak. I won't deny that it left a very bad impression on me about the open source community, especially as someone who was new to it.
I have only recently learned this and I too was surprised it's not a GNU project, and even more so it's not GPL-compatible.
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.
