"Ruby is about to gain thousands of gems", Charles Nutter twittered a few days ago. What has happened? Last year, Charles started the maven_gem project, "a RubyGems plugin (and a utility) to install Maven artifacts as RubyGems", and he now apparently succeeded in making maven artifacts installable as RubyGems, as this shell session shows. This really would make a slew of libraries available to be used in JRuby projects.
Contrary to what's written in the maven_gem Readme file, it seems to be possible to just create a Gem without installing it.
A related new project is JavaGems. It's goal is to be a simpler alternative to Maven for JVM languages, not a replacement, as noted in their FAQ:
Maven is fine. It's an incredibly powerful tool with a lot more features than JavaGems will probably ever have. If Maven is working for you, keep using Maven. The problem is, some of us have smaller needs and don't need all the power of Maven, but rather, need something more simple. JavaGems aims to fill that gap. It's not trying to replace Maven, but rather, complement it.
JavaGems is essentially a Gemcutter instance providing, at the moment, artifacts such as JRuby, Clojure and several Scala libraries. It uses RubyGems and Bundler for dependency management. To see JavaGems in action, this blog post shows how to install Clojure, Compojure (a Clojure web framework) and get a "Hello World" example running in a few easy steps.
In other JRuby related news, JRuby's Java integration will soon be able to generate classes that implement Java interfaces and extend Java classes, as shown in this JRuby example.
For more information on the interaction between Clojure and JRuby, see JRuby and Clojure - A Good Match? on InfoQ.