What is Rubinius ?

Evan Phoenix's Rubinius project is an effort to implement Ruby using as much Ruby code as possible. It is not, as professed, "Ruby in Ruby" anymore. Rubinius started out as a 100% Ruby implementation of Ruby that bootstrapped and ran on top of MatzRuby. Over time, though the "Ruby in Ruby" moniker has stuck, Rubinius has become more or less half C and half Ruby. It boasts a stackless bytecode-based VM (compare with Ruby 1.9, which does use the C stack), a "better" generational, compacting garbage collector, and a good bit more Ruby code in the core libraries, making several of the core methods easier to understand, maintain, and implement in the first place.

The promise of Rubinius is pretty large. If it can be made compatible, and made to run fast, it might represent a better Ruby VM than YARV. Because a fair portion of Rubinius is actually implemented in Ruby, being able to run Ruby code fast would mean all code runs faster. And the improved GC would solve some of the scaling issues Ruby 1.8 and Ruby 1.9 will face.

Rubinius also brings some other innovations. The one most likely to see general visibility is Rubinius's Multiple-VM API. JRuby has supported MVM from the beginning, since a JRuby runtime is "just another Java object". But Evan has built simple MVM support in Rubinius and put a pretty nice API on it. That API is the one we're currently looking at improving and making standard for user-land MVM in JRuby and Ruby 1.9. Rubinius has also shown that taking a somewhat more Smalltalk-like approach to Ruby implementation is feasible.