100% pure-Java implementation of Ruby

 JRuby is a 100% pure-Java implementation of the Ruby programming language.
 .
 JRuby provides a complete set of core "builtin" 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 JRuby hopes to
 implement as many as is feasible.