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Dual licensing is used to maximize compatibility. One requirement is that licenses must be non-exclusive, although they don't have to compatible and as licensee you are free to choose a subset of the licenses when publishing your own work.

With non-exclusive I mean that you don't give up rights to license the work to others under other licenses in any way.

I wondered, if one could actually maximize this, e.g. create some kind of "omni" license that includes all possible non-exclusive licenses at the same time? Something along the lines of:

Omni-license: This work is multi-licensed under all non-exclusive licenses that ever existed or will ever exist. This includes but is not restricted to all past and future variants of GPL, LGPL, BSD, MIT, CC and the Public domain (wherever it exists).

The second part should not be necessary, it's here just for illustration of the idea.

Question is if that would work (maximizing compatibility, not creating other problems on the go)? If not, why not?

I imagine that derivative works could then also be distributed under the Omni-license or could be distributed under any (set of) non-exclusive license(s) and Omni-licensed material would be compatible with all non-exclusive licenses by design.

If it doesn't work, could one at least just compile a really big list of existing non-exclusive licenses and create a multi-license containing them? Something like

Any-license: This work is multi-licensed under GPL-2.0, GPL-3.0, MIT, 3-clause BSD, ...

where one could just link to the texts of the respective license. Or would the full texts need to be included (could probably be done with reasonable effort)?

  • I see a nice way to get free income here: 1. You create something that is licensed with this "Onmi-license"; 2. I create a new (non-exclusive, non-free) license with a clause stating that everyone distributing a work covered by this license must pay me X USD; 3. I send you a bill for distributing a work covered by my new license. – Bart van Ingen Schenau Aug 21 at 16:33
  • @BartvanIngenSchenau: I see the problem. That probably kills the all possible licenses. One could maybe try to exclude such cases but it might be too risky. A long list of included licenses might be a better option then. – Trilarion Aug 21 at 16:36
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    I don't understand the advantage of this versus simply using a maximally permissive license like CC0 (which would be included in the set of allowed licenses anyway). If you want downstream distributors to use any license, use a license yourself that doesn't prohibit that. – apsillers Aug 21 at 18:12
  • @apsillers is it clear that CC0 is compatible with all the usual licenses? The advantage would probably be to make that explicitly clear. – Trilarion Aug 21 at 18:53
  • How will you explain or dictate the "non-exclusive license" requirement in your license agreement? If you want to dual or multi license, then it would be clearer to say specifically which licenses. Just as an example, GPL with the "upgrade option" includes the phrase "or (at your option) any later version" which gives licensees the choice between GPL v2, GPL v3, or some later version. – Brandin Aug 22 at 7:50
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It would certainly "work", you can place any license you want (even several) on your work. But the end result is that of the most liberal of all of them (why should I select, e.g. GPLv3 when you offer me public domain?).

Select your license(s) with care. Look at David Wheeler's "Make Your Open Source Software GPL-Compatible. Or Else.", check out Choose an open source license, take a look at OSI's discussion of licenses.

  • The idea was to maximize compatibility explicitly and right out of the box. You could choose public domain or GPLv3 or both or something else, I wouldn't care. – Trilarion Aug 30 at 9:05
  • "Most compatible" is public domain, but that is not applicable everywhere. Next would be MIT/BSD. But that means maximally giving up rights. – vonbrand Aug 30 at 12:17

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