Re: Elisp licensing

[Richard Stallman]

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  > I was wondering if somebody could clarify, from a legal perspective,
  > and from the perspective of the Gnu project, what is acceptable
  > licensing for Elisp code?

Those two perspectives make two different questions -- which are you
asking?

                              In my personal observations, finding Elisp
  > in the wild, it seems like most people are labeling their Elisp as
  > GPLv3+,

That is what we recommend.

            not counting the code that doesn't have any license attached
  > at all.

A nontrivial file with no license is nonfree.  That is the default under
copyright law.

When you see an instance of that, please point this out to the auhor
and ask per to add a GPLv3+ license header.

  >  But recently I came across an Elisp library marked LGPLv3+,

LGPLv3+ is basically the same as GPLv3+ ecept that it gives some
additional perissions.  (Please read it for yourself so you will see:
https://gnu.org/licenses/lgpl-3.0.txt.)  So it is no problem.

  > and also another project that was under an ISC license.

That is a weak, permissive license, compatible with everything.  We do
not recommend it but its use is not a problem.

  > My understand was that nearly all Elisp programs heavily utilize the
  > Gnu Emacs API and libraries, and so they should be also licensed under
  > GPLv3+.

Legally they need to be under licenses compatible with GPLv3+,
if they are meant for use in combination with GNU Emacs.
Morally, it is always good to use GPLv3+, and there is rarely
a good reason to use anything else.  

I suggest you read https://gnu.org/licenses/license-compatibility.html
to learn about license compatibility issues.

  >  Maybe with exceptions for programs written for Guile Elisp

That is rather vague, so I won't say it is absurd, but why would
it ever be better to use a weaker license for Emacs Lisp code?
Copyleft supports freedom, so in general it is better to copyleft
a program than not to.

                                                                or
  > one of the non-Gnu Emacs clones that are being developed, like Gypsum
  > or Rune.

What are those?   Why would they make it better not to uee copyleft?

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)