Per Bothner is really an amazing programmer. Kawa, which
started out as a Scheme implementation (written in Java and
compiling Scheme code to Java Virtual Machine byte codes)
intended for DSSSL processing, is slowly becoming a high
performance language implementation framework, a source of
generally useful Java code, and the underpinnings of a JVM
& Swing based Emacs.
Kawa Scheme is quite a dandy Scheme--fast, portable, and well
integrated with Java. Indeed, I'd have to label it the premier
"other langauge" implementation for the JVM (with, uh,
Java being the premier language implemention for the
JVM, period).
You can get some teasers for JEmacs at the JEmacs SourceForge
page, including some screen shots. Bothner plans to add an
Emacs Lisp compiler to Kawa so that all your favorite Emacs
packages will run, plus you can write new ones in Scheme (or,
one would expect, any JVM based language!)
Keep an eye on it, all you Java, Scheme, and Emacs junkies.