One of the fascinating trends that the Java world has seen in the last few years is the growth of non-Java languages that use the JVM (Java Virtual Machine). After all, if you create a new programming language, you will need to write it for a particular platform. If you want your language to be portable across platforms, you will need to implement versions for each of those platforms. By contrast, if you implement your language on the JVM, then your language will work on any system with a JVM, which is basically everywhere. Four of these languages -- Jython, JRuby, Groovy, and Scala -- are released under open-source licenses, and are increasingly popular choices for programmers who value portability.