This library is called gtk_paradise (release saga 0.11.x), the successor to the older gtk_module project. The gtk_paradise library extends the Gtk/Gdk part of ruby-gtk - in particular for ruby-gtk2, ruby-gtk3 and ruby-gtk4. This gem includes some add-on colours, helper-methods to different GTK-widgets as well as extensive CSS rules that could be used "from the get go" (for ruby-gtk3 and ruby-gtk4). See the online-documentation of this gem for more information in this regard. The central idea powering this gem is to make the ruby-gtk bindings more "ruby-like" rather than retain them to be a 1:1 mapping to the underlying C source code. The custom widgets bundled into this gem are an attempt to further make working with the ruby-gtk bindings easier. That way, the time investment by users of this gem is reduced, such as when they wish to create new applications and new projects from scratch. This project is still rather beta-ish, though. APIs may change a lot, still - do not expect stability for the time being. It is not recommend to use this project in production yet, unless you are willing to see things potentially break all over everywhere, every now and then. Long-term stability is planned in the long run, though. Once achieved it will be announced on the README.md as well as enter the 1.0.x release series. For more information pertaining to this project, please have a look at the documentation for this gem, at: https://www.rubydoc.info/gems/gtk_paradise/