Ruby is an excellent choice for building desktop apps with a native GUI (Graphical User Interface) that looks familiar on Mac, Windows, and Linux. In fact, Ruby pushes the boundaries of developing such apps in brand new ways not seen in web development by supporting very lightweight and declarative GUI syntax including bidirectional data-binding, thanks to Glimmer DSL for LibUI, a gem that won a Fukuoka Ruby 2022 Special Award. In this talk, I will cover concepts like the GUI DSL, data-binding, custom controls, area graphics, drag & drop, MVC/MVP pattern, and scaffolding, with sample demos.