A dual license system for code libraries?

[Carsten Agger]

On 02/26/2017 10:09 AM, Simon Hornbachner wrote:
> Honestly, I don't think you'll find one, for the reasons I mentioned
> earlier. For any NPO with the main goal to protect and strengthen Free
> Software, buying yourself out of the need to comply with the GPL would
> just be inherently at odds with their core mission.
>
> I understand that telling proprietary vendors to either "deal with" the
> GPL or go away feels like a waste of ressources and opportunity, but I
> honestly believe that any other position leads us down a very very
> slippery slope that in the end will not lead to more free software, but
> a weaker, watered-down version of copyleft that I personally wouldn't
> want.
>
>

IANAL and I'm unaware of the finer legal intricacies that might apply.

But maybe Agner might consider using the Mozilla Public License 2.0? It 
differs from the GPL and LGPL in that

* it is a strong copyleft
* it applies on a per file basis, meaning that only files that you 
actually changed are affected by the copyleft.

Thus it's permitted to build a proprietary application (a derived work, 
I believe it would be) which uses the MPL library - any changes to the 
library itself, indeed to any files covered by the MPL, need to be 
distributed under the MPL.

So changes to Agner's library would remain free software, but people can 
use it to build proprietary application which they supply in other files.

Best
Carsten