Ruva is a simple stack-based virtual machine implementation written entirely in Ruby. It loosely follows the JVM specification, with the aim of being ?compatible enough? to run standard Java(tm) class files (compiled with, for example, Sun?s javac). Please note, however, that Ruva is not a Java(tm) Virtual Machine, and is not certified or endorsed by Sun Microsystems.
http://ruva.rubyforge.org/