From Rosetta Code
Rubinius is an implementation of Ruby. Other implementations of Ruby.
<lang ruby>p RUBY_ENGINE
  1. => "rbx"</lang>

Rubinius is a Ruby interpreter that translates Ruby to LLVM bytecode, and then to native machine code. Rubinius also implements most of the core library in Ruby. It also has its 'actor' library.

Rubinius 1.2.x only implements Ruby 1.8.7, it cannot run Ruby 1.9 code.