> When you read the gnuplot license, you should be aware that you are
> reading a document from more than 25 years ago.
This is not true. Gnuplot was actually relicensed in 1998, for version 3.7 (the previous license didn't permit to distribute modified binaries at all). It is a bit sad that such an obnoxious clause was introduced at the time when the benefits of free software should have been already obvious.