This library is called gtk_paradise (release saga 0.8.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 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 have them a 1:1 mapping to the 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. This project is still rather beta-ish, though. APIs may change a lot still. Do not yet use it in production unless you are willing to see things break all over everywhere every now and then. Long-term stability is planned in the long run, though. For more information, please have a look at the documentation for this gem, at: https://www.rubydoc.info/gems/gtk_paradise/