Notes from TheServerSide Java Symposium, March 2009
Why Ruby? He talks about the known good language features, but the biggest reason is Rails. Ruby is actually an older language than Java.
JRuby 1.1 incorporates a just-in-time (JIT) compiler, and in many tests is faster than the Matz Reference Implementation.
In answer to a question, JRuby would exclude some gems [...]