First of all, apologizes for the self promotion, but the users feedback is the best way to catch bugs and get new ideas.
I've released a jruby gem to use an embed Tomcat to develop rails applications, as we do with mongrel, webrick or jetty. The project is built in top of jruby-rack and you can grab it from github,
it's web page is:
and you can take a look at the source code here:
Please, feel free to send me bugs, feedback, comments or whatever. At the moment the project has just been tested with a really basic application.
Cheers