Rubinius
Rubinius is an alternative Ruby implementation created by Evan Phoenix. Based loosely on the Smalltalk-80 Blue Book design, Rubinius seeks to
"provide a rich, high-performance environment for running Ruby code."
Goals
Rubinius follows in the Lisp and Smalltalk traditions, by natively implementing as much of Ruby as possible in Ruby code.It also has a goal of being thread-safe in order to be able to embed more than one interpreter in a single application.