Doubleshot will download dependencies on demand, compile your Java sources and let you spend most of your time in Ruby without having to juggle two different dependency management tools, different build tools and being forced to execute your code through Rake or Maven based tools.

Cotton is a JRuby exclusive Web Application Framework. It takes the best of Ruby frameworks, like REST style routing, asset packaging and mountable apps, and adds a few tricks of it's own like first-class Forms, clustered caches and Sessions, and performance++. We aim to ensure Cotton is the fastest platform for Ruby on the Web, period.

MailBuilder is a simple library for building RFC compliant MIME emails.

OnChange is a File System Monitor for JRuby/Java similar to the Listen or Watchr gems. Since the underlying library used is Java7's WatchService, it's Ruby support is limited to JRuby, and you must be running Java7.