It is an installer that greatly simplifies the JRuby installation.
Edit by : The BitNami JRubyStack is an installer that greatly simplifies the installation of jRuby and its runtime dependencies. It includes ready-to-run versions of JRuby, Rails, Java, Tomcat, GlassFish gem, MySQL and Subversion.

JRuby is a 100% Java implementation of the Ruby programming language. It is Ruby for the JVM. JRuby provides a complete set of core builtin classes and syntax for the Ruby language, as well as most of the Ruby Standard Libraries.

With JRubyStack you can:
-Develop your JRuby on Rails application using Java from Ruby.
-Launch your application with the GlassFish server thanks to the GlassFish gem.
-Make a .war file out of your application in 3 simple steps (see Quick Start Guide for Details).
-Deploy it to the bundled Tomcat.
-Commit and Checkout your code with the subversion client.

New:
* Updated jruby (1.1RC2 -> 1.1.4)
* Updated rails (2.0.2 -> 2.1.0)
* Updated gem ActionMailer (2.0.2 -> 2.1.0)
* Updated gem actionpack (2.0.2 -> 2.1.0)
* Updated gem ActiveRecord (2.0.2 -> 2.1.0)
* Updated gem activerecord-jdbc-adapter (0.7.2 -> 0.8.2)
* Updated gem activerecord-jdbcmysql-adapter (0.7.2 -> 0.8.2)
* Updated gem activeresource (2.0.2 -> 2.1.0)
* Updated gem activesupport (2.0.2 -> 2.1.0)
* Updated gem jruby-openssl (0.1.1 -> 0.3)
* Updated gem rspec (1.1.3 -> 1.1.4)
* Updated gem warbler (0.9.3 -> 0.9.10)
* Added gem_highline (1.4.0)
* Added gem_echoe (3.0)
* Added gem_rubyforge (1.0.0) you can free download JRubyStack 1.2-0 nojdk now.