Ruby is a dynamic, reflective, general purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto. It was influenced primarily by Perl, Smalltalk, Eiffel, and Lisp.

Ruby supports multiple programming paradigms, including functional, object oriented, imperative and reflective. It also has a dynamic type system and automatic memory management; it is therefore similar in varying respects to Python, Perl, Lisp, Dylan, Pike, and CLU.

Features

Ruby has exception handling features, like Java or Python, to make it easy to handle errors.

Ruby features a true mark-and-sweep garbage collector for all Ruby objects. No need to maintain reference counts in extension libraries. As Matz says, “This is better for your health.”

Writing C extensions in Ruby is easier than in Perl or Python, with a very elegant API for calling Ruby from C. This includes calls for embedding Ruby in software, for use as a scripting language. A SWIG interface is also available.

Ruby can load extension libraries dynamically if an OS allows.

Ruby features OS independent threading. Thus, for all platforms on which Ruby runs, you also have multi-threading, regardless of if the OS supports it or not, even on MS-DOS!

Ruby is highly portable: it is developed mostly on GNU/Linux, but works on many types of UNIX, Mac OS X, Windows 95/98/Me/NT/2000/XP, DOS, BeOS, OS/2, etc.

References:https://www.ruby-lang.org/en/

Platform:unknown ; License:MIT/X Consortium License

References:https://flexmock.rubyforge.org/

Watir drives browsers the same way people do. It clicks links, fills in forms, presses buttons. Watir also checks results, such as whether expected text appears on the page.
Watir is a family of Ruby libraries but it supports your app no matter what technology it is developed in. Like other programming languages, Ruby gives you the power to connect to databases, read data files and spreadsheets, export XML, and structure your code as reusable libraries. Unlike other programming languages, Ruby is concise and often a joy to read.
Platform:Cross Platform ; License:unknown
Reference:https://watir.com/

Use RDE like a favorite Editor.
Do execute ruby scripts from editor without saving files and get the result without dos console. 
Write scripts easily with HTML Help link, Input support features.
Edit the editing text with ruby on RDE.
Debug the scripts on RDE.
Platform: Windows ; License:no
Reference:https://homepage2.nifty.com/sakazuki/rde_en/index.html

RubyScript2Exe transforms your Ruby application into a standalone, compressed Windows, Linux or Mac OS X (Darwin) executable. You can look at it as a "compiler". Not in the sense of a source-code-to-byte-code compiler, but as a "collector", for it collects all necessary files to run your application on an other machine: the Ruby application,the Ruby interpreter and the Ruby runtime library (stripped down for your application). Anyway, the result is the same: a standalone executable (application.exe).And that's what we want!

Platform:Cross Platform(Windows,Linux,Mac);License:GNU General Public License (GPL) version 2

References:https://rubyforge.org/projects/rubyscript2exe/

Platform:OS Independent; License:GNU Lesser General Public License(LGPL)

References:https://rubyforge.org/projects/ttk

Platform:unknown ;License:MIT/X Consortium License, Ruby License

References:https://mocha.rubyforge.org/