Groovy is, as the official site puts it, "a new agile dynamic language for the JVM combining lots of great features from languages like Python, Ruby and Smalltalk and making them available to the Java developers using a Java-like syntax." It's completely compatible with Java, but it adds a wealth of helper methods and language constructs that can dramatically reduce the amount of code. For those who love languages like Ruby but need a closer relationship with the Java Virtual Machine, Groovy is wonderful.
Xcode Language Specification
SubEthaEdit 2.0 Mode
Provides basic code-coloring and navigation support for Groovy in the SubEthaEdit collaborative text editor. For SubEthaEdit version 2.0 and higher.