FXRuby

FXRuby is a library for developing powerful and sophisticated cross-platform graphical user interfaces (GUIs) for your Ruby applications. It’s based on the FOX Toolkit, a popular open source C++ library developed by Jeroen van der Zijp. What that means for you as an application developer is that you’re able to write code in the Ruby programming language that you already know and love, while at the same time taking advantage of the performance and functionality of a featureful, highly optimized C++ toolkit.
(Link: FXRuby)