I started to using the useful Intro.js library in my project, but after few months use I updated it and found that the license changed on 08/03/2016.
The library is definitely open source and free software, but at the same time if I want use it for commercial use it seems I need to pay a license fee. Why is this required if the code is open source?
Maybe I'm missing something because I'm new in the license use world.
From their website:
Intro.js is a free and open-source library, however, if you are using the library for your business you can subscribe to one of commercial licenses plus support, code review and support by Intro.js team.
Being open-source doesn't mean that everything has to be free, open-source software can be sold and used in general commercially. Also, commercial open-source applications are a part of the software industry for some time.
You can read all the information about selling open source software right here.
I'm Afshin, the author of Intro.js
Intro.js is open-source and it will be free to use for everyone. I recently added a commercial license to the project to provide a better support, versions, etc. So, if you are using the project in a commercial app/theme/plugin you need to have a commercial license.
I suggest reading this as well: https://en.wikipedia.org/wiki/Business_models_for_open-source_software
来源：https://stackoverflow.com/questions/36158360/intro-js-is-opensource-or-not