The last release was in 2008-03-06. What happened to it? Is it still under active development? Are there any replacements?
Slightly modified version of Rhino (1.6r2) is part of Java 6 and on top of that from what I've tested Rhino is very much feature complete so there really isn't anything left to develop onwards, apparently it's also quite bug-free also.
I'd say Rhino is one of those rare libraries which are actually done.