It's built on top of the Smalltalk VM concept.
Here are some key features of "Rubinius":
· Generational garbage collection
· Just-In-Time compilation
· Compatibility with existing C APIs
· Bytecode virtual machine
· Bytecode compiler
· Supports Ruby 1.8.x
· Ruby 1.9.2 or higher
· No Windows support.
· No Ruby 1.9.x support.
What's New in This Release: [ read full changelog ]
· Contains a large number of bug and compatibility fixes as well as a handful of performance improvements.