Cross-platform development with JRuby and Swing is an article from 2008 for IBM developerWorks.
In addition to building Web and console applications with Ruby, you can write complex GUI desktop applications that run unmodified on multiple platforms. Thanks to JRuby, a robust alternative to the traditional C implementation of Ruby, Ruby GUI toolkits can use UI tools available to the Java™ platform. This article introduces Monkeybars, a library that uses JRuby and Swing for building applications, and takes you through an example application.