Javascript shell with Rhino
The Rhino javascript interpreter (from Mozilla, sister to SpiderMonkey) has an interactive mode:
C:\dojo\buildscripts>java -jar lib/js.jar
Rhino 1.5 release 3 2002 01 27
js> print('boo');
boo
js>
The Rhino jar is a part of the dojo distribution, so if you've got dojo (from SVN, not the pre-built releases) you already have it.
The Scripting Java page from Mozilla has these and other details. After all these years, javascript is finally able to script java. I find that amusing even if no-one else does :)
(yes I know LiveConnect has been around for almost as many years, probably what I mean is finally there's a practical environment that enables useful work to come from scripting java). Also, as running my javascript scripts is now possible from the commandline, I can invoke them easily from perl, my editor, SlickRun, etc. Which, as redundant as that sounds, is bound to be handy.
Here's another article on the Javascript CommandLine, and lots more