I stopped reading it after it said concurrency in Ruby was "N/A". That's a silly statement for a language that has threads and coroutines built in, as well as a number of event loop and actor libraries.
When run on JRuby, threads also offer parallelism.
When run on JRuby, threads also offer parallelism.
http://ruby-doc.org/core-2.2.0/Thread.html
http://ruby-doc.org/core-2.2.0/Fiber.html