Last night I presented an Introduction to JRuby at the Philadelphia Java Users Group. My goal was to introduce Java programmers to Ruby and get them to how features of the language allowed for functionality and code structure that is not possible in Java alone. While I did talk about Rails at the end, my point was to get the developers to understand that the meta-programming functionality in Ruby allows for both plugin develeropers and users of Rails to extend and improve the base platform in many interesting ways.
The presentation is available at http://www.innovationontherun.com/presentation-files/Introduction%20to%20JRuby-10-23-2007.pdf and the associated source code can be found at http://www.innovationontherun.com/presentation-files/JRuby-JUG.zip. If you are looking at the source code, start with the file ABOUT.txt. It describes the prerequisites needed to get the code to run and the order of the listed files follows the order that they were used in the presentation.
If you have questions or comments, feel free to send me an email.