Ruby is a general-purpose programming language created by Yukihiro “Matz” Matsumoto and public since 1995. Programs need no variable declarations, and the reference implementation, CRuby (also called MRI, Matz's Ruby Interpreter), is written in C. The latest version on the official site is 4.0.9.
In Ruby everything is an object, including numbers, so every value has methods. A block is a piece of code (a closure) passed to a method, so that methods such as each or map run custom code on every item. A class has single inheritance, and modules add shared methods to classes as mixins. Ruby also has exception handling and a mark-and-sweep garbage collector, which frees unused memory automatically. Libraries are packaged as gems; the site counts over 200,000 gems. The best-known software written in Ruby is Ruby on Rails, a framework for web applications. Other implementations run Ruby on the Java Virtual Machine (JRuby) or embed a small Ruby inside an application (mruby).
Ruby is free and open source: free of charge, and free to use, copy, modify and distribute.