JRuby provides a complete set of core "built-in" classes and syntax for the Ruby language, as well as most of the Ruby Standard Libraries. The standard libraries are mostly Ruby's own complement of .rb files, but a few that depend on C language-based extensions have been reimplemented. Some are still missing, but we hope to implement as many as is feasible. JRuby is designed to provide you with an easy to use implementation of Ruby completely written in Java.