MRI

MRI is an implementation of Ruby. Other implementations of Ruby.

Matz's Ruby Implementation or MRI is the original Ruby interpreter by Yukihiro Matsumoto, the inventor of Ruby. Matz and contributors wrote the interpreter in C language; MRI is also known as C Ruby or CRuby, by analogy with CPython.

MRI is the original Ruby. When you download Ruby, you downloaded MRI; when you report a bug in Ruby, you reported a bug in MRI, and so on. There are now other implementations of Ruby that follow the same language as MRI.

When an example on Rosetta Code works with Ruby 1.8.7, this can be MRI 1.8.7, or anything else that implements the same language.