How do I tell which Ruby interpreter I'm using?

I've seen this thread, but my question is maybe more basic:

Given that the response from the accepted answer in that thread[1] is for me, "/Users/username/.rvm/rubies/ruby-2.3.0/bin/ruby", how do I know if that's MRI, JRuby, etc? What would it look like if it were each of the other major interpreters?

[1] To save a few seconds, RbConfig.ruby

Nowadays, all mainstream Ruby implementations set the RUBY_ENGINE pseudo-constant. The values for the various implementations which I can remember off the top of my head are:

• Rubinius: rbx
• JRuby: jruby
• TruffleRuby: truffleruby
• Opal: opal
• MRuby: mruby
• YARV: confusingly, ruby
• MRI: even more confusingly, also ruby
• MagLev: maglev
• IronRuby: ironruby
• MacRuby: macruby
• Topaz: topaz