This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
To answer David's question, the only other JVM language we cover integration with in the book is Java, which is a very common use case. A lot of the other JVM languages are targeted at server-side Java applications which you can transparently integrate with using Java's web service support.
Griffon is an interesting case where Andres and the team have been doing some interesting client integration work between JavaFX and Groovy. It is still in the early stages, but I think there are some interesting possibilities down the road from an alternate Groovy-based DSL for JavaFX to a Grails-like application templating system for quickly building large JavaFX applications.