Ruby has a core library that is part of the interpreter and always available. It’s classes like String and Time. But what would it be like if we re-implemented the core library, writing it in Ruby itself, and made it available as a gem? Would it be faster or slower? Would it be easier to understand and debug? What other benefits could there be? It was originally Rubinius that implemented Ruby’s core in Ruby, and it has been taken up and maintained by the TruffleRuby team.