I want to develop and distribute a GUI (Graphical User Interface) for an existing command-line tool (LibLouis). I want to do so using .NET WPF or Windows Forms, but the library of Liblouis is written in C++ and I do not have the possibility to merge C# and C++ as far as I know. The library was licensed under the LGPLv2.1+, so that would have been nice, if I could use it.

Unlikely, I had to decide to use the command-line tools, which are licensed under the GNU General Purpose License (GPLv3+) license.

My question now is: can I create a GUI for those command-line tools and sell this GUI under my own propretary license?


As long as you do not change nor distribute any code that is licensed under LGPLv2.1+/GPLv3+ - you can. This means you only sell and distribute your (or permissive open source) code. Restrictive licenses apply to you only if you have to go into their files and code. If you can keep them separate then you're clear.d you shoukd be able to

Edit: Legally speaking GPL is no different from LGPL an does not prohibit you from linking with your own code as long you keep your code in different files. Under GPL you are obligated to distribute their source whether you change anything there or not. But you can still license your own code in different files under different license. At least that's how copyright law works. But being legal and all doesn't protect you from being sued since people have different understanding (or lack thereof) of the law. So while you can be right, be prepared to fight ignorant bullies, that's all.

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  • Is it allowed to bundle the two in an installation wizard? – Jordy Deweer Apr 14 '19 at 13:59
  • Bundling would mean distributing their code. This means you are obligated only to share their source. In theory it should work but GPL folk are notorious for not understanding how copyright works. – Smart455 Apr 14 '19 at 14:20
  • @JordyDeweer yes, you can distribute together - the Open Source Definition defines this as one of the freedoms. See #9 - opensource.org/osd-annotated – ivanivan Apr 14 '19 at 15:08
  • @ivanivan This freedom comes from the law and without the misinformation and outright lies from the FSF, OSI wouldn't have to confirm these freedoms. Not to mention that Gnu wouldn't exist if they wouldn't have used UNIX code side-by-side. – Smart455 Apr 14 '19 at 17:12

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