TwentyTwenty uses Zurb’s TwentyTwenty script, located at http://github.com/zurb/twentytwenty/. It is open source software. I have not heard of the paid plugin that is linked in this support question, and would always recommend considering free, open source software where possible.
Yeah we had a long discussion about that over in the Fb group. It turns out someone had almost copied everything from your plugin and simply uploaded it for sale on CC.
A few things: YOU gave Zurb credit. They did not (originally)
It might have been nice if those guys had given YOU credit (but they did NOT)
Their plugin almost line per line, folder names, folder structure, code and almost everything was simply a duplication of your plugin.
After I looked at their code some more, I sent CodeCanyon a message and asked them to look at both your plugin AND the original stuff from Zurb, mentioning that either (or both) an MIT license, or mention to you, and/or Zurb should be included with their ‘paid’ plugin.
CodeCanyon took the plugin down, and then put it back up once the author had included licenses.
Drama.