First of all (as a curiosity) please answer me something.
Can PURE Ruby be used to make GUI without using other libraries or tools?
Now let's get down to business.
I use Ruby 2.5.3 and because I have a project whose graphical interface is very complex, Qt doesn't work for me, the truth is I see it very limited and besides its license doesn't suit me.
The target OS is preferably Linux but if it works with other platforms there is no problem.
It doesn't matter if the tool to use is difficult, what matters to me is that:
* Have official and complete documentation.
* That you have a very large number of widgets.
I saw some gems that were easy to build GUI but very limited so I discarded them.
There is someone who told me that I should learn C and create the GUI with that language and combine it with Ruby, I have no problem with learning C but I don't see how I can combine the two, I've never mixed programming languages but what do you think? Is it possible to do it?
Anyway for now more important is to work alone with Ruby.