This is very interesting: http://salama-vm.org/index.html
Rails has evolved tremendously from what was already a good start. All the development around it has nurtured ruby developement in all areas. Rails and all those parts make up a most mature and advanced software system.
The “rails effect” is due to the accessibility of the system, imho. Ie it is written in ruby.
Ruby itself has not enjoyed this rails effect, and that is because it is written in C (or c++)
I think rubinius started life trying to be ruby in ruby (except for a very small stack handler written in C). It didn’t pan out, but much of it’s early work was based on smalltalk (which is why I think I remember that). And I think all the core Rubinius libraries are written in ruby.
The core classes in Rubinius are mostly written in ruby itself.
The VM, JIT and some parts of the core classes (called Rubinius primitives) are written in C++.
Rubinius Kernel / Core Classes: https://github.com/rubinius/rubinius/tree/master/kernel
Rubinius VM: https://github.com/rubinius/rubinius/tree/master/vm
Rubinius Primitives: https://github.com/rubinius/rubinius/tree/master/vm/builtin
Also the entire Stdlib for rubinius is outsourced into gems: https://github.com/rubysl
I guess my point was that this was not always so. Ruby in Ruby is a cool idea, but is somewhat elusive at this point. Be great is someone could pull it off.
@kofno sorry I misread your reply 
@AstonJ as far as I know Rubinius X will be non compatible with MRI
Rubinius 3.0 should be compatible with MRI but also provide addtional functionality
You can read more about it here: http://rubini.us/2014/11/14/rubinius-3-0-part-5-the-language/
Also you could ask brixen more about this on the rbx gitter channel: rubinius/rubinius - Gitter
Cheers
No worries. I wasn’t especially clear, so I thought I would clarify.