The ease of pairing JRuby with custom Scala/Java and the vast array of Java libraries is amazing. While in the past polyglot either involved SOA or complex integration using C-based glue code and lots of wrappers, this stuff just snaps together like lego bricks. Fantastic. I recently wrote a JRuby project built ontop of two Java libraries and it couldn't have been any easier. Require the jar and you can just start creating and interacting with the classes inside.<p>I would like to see a way to more quickly build and maintain Java/Scala code for existing JRuby projects. It's a big deal to have to learn the entire Java package and build workflow if you just want to write a single class to accelerate a section of Ruby code.