The last while I have been developing on a new scripting language to be used with the Script Engine API (JSR 223). It's called Artifact and is fully compatible with Java source code, as it first transcompiles to Java source code. When it compiles Java source code, it uses the Java Compiler API (javax.tools and friends) provided with the JDK. So you will need the tools.jar to run it.
To read more about it, you can do so on my GitHub project page, that can be found at http://www.github.com/WavePropagation/org.cel4j.artifact
Do you think this could be useful in a game? Or maybe you know some awesome feature, that could be useful for scripting in games?