What I'm looking for is a scripting engine for Java that would allow users to write simple scripts to control the behavior and events for a game. Something that:
is simple - something easy to pick up, especially for people with some basic programming/scripting experience
provides lots of control - I can easily start/stop/pause scripts and control how much execution time each gets, perhaps how much memory space they can use
is separated from the Java environment itself - No access from scripts to any Java objects or classes, only to those functions I explicitly provide
I'd also consider developing my own language with something like ANTLR, but it's probably more effort than I want to put in.