I use Ruby from a user level and really don't deal with the internals. I have know Rubinius as 'Ruby in Ruby' which I assumed was a generalization. Recently, I got an error with Rubinius in the RubySL (no, I don't have error msg).
I started looking at RubySL and was a little surprised to see Rubinius everywhere. I really like Ruby and was just curious why Rubinius is in most of the RubySL? It seems to be used with things like locks / unlocks (such as https://github.com/rubysl/rubysl-thread/blob/2.0/lib/rubysl/thread/thread.rb ). Definitely not questioning it, just curious.
RubySL is short for Ruby Standard Library. It is a basic part of the shipped code bundle which forms what is generally known as Ruby. The standards library provides rather basic stuff you often need but which doesn't need to be part of the core language.
For example, the implementation of the Hash or Array, the language keywords, how assignment works, ... are part of the core language. These are often implemented in a language other than Ruby. MRI (the common C-Ruby) implements this mostly in C, JRuby implements this in Java. Rubinius implements this patly in C++ but mostly in Ruby itself. It can do this by bootstrapping itself from a very simple base VM and gradually adding more stuff with Ruby.
The standards library however is mostly implemented in Ruby in all implementations (with some exceptions mostly for performance reasons). Now, all Ruby implementations right now have their own implementation of the Ruby standards library which can thus differ in minor details.
Rubinius' approach to implementing a standards library was to implement it as separate gems. The idea was to one day provide a common standards library which could be used by other implementations (including MRI). This is in line with the efforts of esp. the Rubinius community to drive the RubySpec project in order to provide a common language specification and test suite for all Ruby implementations.
The RubySpec project was eventually abandoned and right now, it doesn't seem as if other Ruby implementations seem to be moving to the RubySL gems for implementing their standards library.
Thus, (and this is the TL;DR), the RubySL gems implement the Ruby Standard Library for the Rubinius project. Thus, it is expected to see the Rubinius project all over the place there: it is their code which is generally not used by other Ruby implementations.