This library is called gtk_paradise, the successor to the older gtk_module project. It extends the Gtk/Gdk part of both ruby-gtk2 / ruby-gtk3, including some add-on colours - see the online-documentation for more information in this regard. The basic idea behind this gem is to make the ruby-gtk bindings more "ruby-like" rather than have them a 1:1 mapping to the C source code. Some custom widgets are also created, to make working with the ruby-gtk bindings easier. This project is very beta-ish, though. Do not yet use it in production unless you are willing for things to break all over everywhere. :) For more information, please have a look at the documentation for this gem, at: https://www.rubydoc.info/gems/gtk_paradise/