Quoting Steve Litt (slitt@???):

> Hi all,
>
> I'm asking this question in a lot of places, but for sure I hold
> Devuan's answer in high regard.
>
> I'm putting the finishing touches on UMENU2, to the point where I'm
> ready to write the COPYING file and mark the Python files with a
> license. I'm considering two licenses:
>
> * Expat license: http://directory.fsf.org/wiki/License:Expat
>
> * GPL Version 2: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
>
>
> A couple notes: The above Expat URL says Expat license is GPL
> compatible. I don't like GPLv3 because it's too complicated and IMHO a
> little too restrictive. Expat's similar to some MIT and BSD licenses
> and the X11 license.
>
> Any opinions on which to choose?

{sigh}

It's really not possible to answer this question properly without your
saying what you're trying to achieve through choice of licence.

GPLv2 is of course the classic copyleft aka reciprocal licence[1].

Expat License is, along with the several variants of the BSD Licence,
the classic permissive aka academic licence. It's a fine licence for
its day and has many compelling wins as a permissive licence. But
there's one important thing I will plead with you about: I had to look
up w.t.f. you were talking about, _even_ though I'm a licensing guy,
because I'd never heard the term 'Expat License' before, and that's your
problem: Nobody knows that name, and it doesn't signify that it might be
the technically correct name for it. _Everyone_ calls it the MIT
License or MIT X11 License. (Yes, it _is_ MIT License.) And that is
why you, too, should reference it as 'MIT License'.

MIT Licence is a unilateral (vice bilateral) contract. It's actually a
cleaned up, i.e., improved version of the BSD License as rewritten by
MIT lawyers, to make it easier to read and understand. Its broader
enumeration of rights granted make it include an implicit patent rights
grant. Also, it explicitly includes the right to sublicense, which
isn't mentioned explicitly in the BSD licences. It also disclaims
(unlike BSD) any warranty that the licensor guarantees non-infringement
of someone else's intellectual property.

Yes, MIT License is indeed GPL-compatible. So are 3-clause and 2-clause
BSD. (But I recommend MIT License over those.)

If you're looking for a thoroughly modern academic (permissive) licence,
look no further than Apache License (ASL) v. 2.0. ASL specifically
addresses trademarks. It is specifically designed to allow derivatives
of ASL-licensed works to be compatible with the licensing of GPL code,
but, annoyingly, only with GPL v.3 code.

According to a survey by Black Duck Software, the most popular open
source licences, in order, are:

MIT License               26%
GPL 2.0                   21%
Apache License 2.0        16%
GPL 3.0                    9%
BSD 3-clause               6%
LGPL 2.1                   4%
Artistic License[1]        4%
LGPL 3.0                   2%
ISC License                2%
Microsoft PL               2%
Eclipse PL                 2%
Code Project Open L 1.02   1%
BSD 2-clause              <1%
CDDL 1.0                  <1%
Affero GPL 3 & later      <1%
Microsoft Reciprocal L    <1%
GPL w/Classpath Exception <1%
WTFPL[1]                  <1%
CDDL 1.0                  <1%

I cite this table of licence popularity (from
https://www.blackducksoftware.com/top-open-source-licenses) to raise the
point that you really want to stick with one of the major licences
unless you have an extremely compelling reason to do otherwise. And the
top three are, obviously, _the_ major licences. Overwhelmingly.

Why might you want GPL 2.0 specifically? That would imply you wish to
enforce reciprocality onto derivative works, i.e. you're not OK with
people creating and sending out proprietary derivatives of your work.
(One use-case for GPL 2.0 or other similar copyleft/reciprocal licences
is as part of a dual-licensing regime to support a proprietary software
business model: You offer the essential code implementing your ideas
to the public under copyleft, which prevents any commercial competitor
from creating proprietary offshoots. Having made your code popular that
way, you _then_ also offer it under proprietary licensing with a bigger
feature set and enhancements, for money. As long as you yourself own
all the needed copyrights, you can keep doing this.)

Why might you want ASL 2.0 or MIT License specifically? That would
imply you want your code to be maximally attractive for third-party
reuse and adaptation, and don't object to proprietary derivatives.


[1] Incompetently drafted licence. Do not use for anything.