Rubinius is a fast implementation of Ruby written mostly in Ruby. There are lots of reasons for being interested in it but the main one is speed. Version 1.1. is new.

Version 1.1. of Rubinius was released via the Rubinius web page. Rubinius is an implementation of the Ruby language for a virtual machine written in C++ designed to improve the overall performance of the language. As compatibility with official Ruby is a stated aim of the project the main benefit from using Rubinius is speed. The new version implements improved JIT compiling and other optimisations to make it even faster. Another objective of the project is to make it threadsafe so allowing it to take advantage of multicore and multiprocessor hardware. 

However most of the language has been implements using Ruby itself and so Rubinius should be easier to modify and extend by a Ruby programmer. Currently the majority of the bytecode compiler and core framework is implemented in Ruby. 

In it currently targets Ruby 1.8.7 and principle most Gems, Rails plugins and C-Extensions just work. The current edition of Ruby is 1.9.2. 

The new version offers a debugger and a new debugger API. 

The project is sponsored by Engineyard.

Clearly if you need a fast implementation of Ruby then Rubinius is worth a look.

Further Reading

Ruby on Rails for Microsoft Developers

Metaprogramming Ruby

JRuby 1.5.0

Ruby: Visual QuickStart Guide

Beginning Ruby: From Novice to Professional