This library is called gtk_paradise (release saga 0.10.x), the successor to the older gtk_module project. The gtk_paradise library extends the Gtk/Gdk part of ruby-gtk (ruby-gtk3 and ruby-gtk2), including some add-on colours and helper-methods to different GTK-widgets. See the online-documentation of this gem for more information in this regard. The basic idea behind 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. Some custom widgets are also bundled into this gem, to make working with the ruby-gtk bindings easier, e. g. less time investment required by users to create new applications and new project from scratch. This project is still rather beta-ish, though. APIs may change a lot, still. It is not recommend to use it 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. For more information about this project, please have a look at the documentation for this gem, at: https://www.rubydoc.info/gems/gtk_paradise/