2.What is GTK? - gizemozgun/GOTK3 GitHub Wiki

Gtk+ is used to create user interfaces. It is a cross and multi-platform toolset that enables you to use with large widgets from small projects to large projects. Although written in C, it can be used in many languages.(C++,Perl,Ruby, Golang ,etc.) Gtk is a free software Project and its also a part of the GNU project. For more detailed information you can visit The GTK Project GTK3 is LGPL licensed, everyone can use it for free.