I have released software on more on one occasion where I have given a
very liberal license (like MIT), and then put a "however, if you like
this, X would be appreciated." I wouldn't consider it unethical if
someone didn't obey the optional request (it's optional for a reason),
however, it does mean that I do genuinely appreciate someone doing X.
So there is a difference between what is legal and ethical, and what is
the nice/friendly thing to do.
-hpa
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