JRuby deployment ecosystem

JRuby deployment options

Jetty based

Jetty7

Mizuno optimized for speed, Jetty 7, async
Kirk A Jetty binding for JRuby

Jetty6

jruby-rack-jetty Basic jetty handler for rack that sits a top of jruby-rack
Jetty Rails if you have problems with 0.8.1 downgrade to 0.6 (worked for me)
jetty-rackup Runs a rack conform application inside jetty web server
rack-jetty Very simple (mostly Ruby) implementation of jetty as a pure Rack adapter

JBoss based

Torquebox nice for the extra enterprisey jbossey features, but you might lock-in if you use them
picard.java It's enterprise! (carllerche)
Aspen a JRuby web server similar to Thin

Tomcat based

Trinidad Simple library to run rails and rackup applications into an embedded Apache Tomcat

Other

Rails-asyncweb (old) "a fast HTTP server"