Ruby and Rails are very popular and that has made for a lot of available online resources for learning and reference purposes. Here you will find resources the PowerRuby team has found useful over the years.
Code Academy - (Interactive) Learn Ruby in the browser without having to install anything on your machine.
Try Ruby - (Interactive) Learn the basics of Ruby quickly.
The Ruby Programming Language - (Book) O'Reilly book on Ruby programming
Sitepoint - SitePoint provides cutting-edge content for web professionals — developers, designers, programmers, freelancers and site owners. Check out their Ruby content.
Mr. Neighborly's Humble Ruby Book - Covers the Ruby language from the very basics of using puts to put naughty phrases on the screen all the way to serving up your favorite web page from WEBrick or connecting to your favorite web service. Written in a conversational narrative rather than like a dry reference book, Mr. Neighborly's Humble Little Ruby Book is an easy to read, easy to follow guide to all things Ruby.
Ruby Koans - The goal is to learn the Ruby language, syntax, structure, and some common functions and libraries. We also teach you culture. Testing is not just something we pay lip service to, but something we live. It is essential in your quest to learn and do great things in the language.
Ruby Monk - (Interactive) Free, interactive tutorials to help you discover Ruby idioms, in your browser!
Why’s (Poignant) Guide to Ruby - Humorous online Ruby book that's free.
Ruby Under a Microscope: An Illustrated Guide to Ruby Internals - (not for beginner) Gives you a hands-on look at Ruby's core, using extensive diagrams and thorough explanations to show you how Ruby is implemented (no C skills required). Author Pat Shaughnessy takes a scientific approach, laying out a series of experiments with Ruby code to take you behind the scenes of how programming languages work.
blocks-Procs-lambdas - Best explanation that Don Denoncourt has read yet on the usage of blocks, Procs, lambas and methods.
RubyGems - RubyGems is a package manager for the Ruby programming language. RubyGems is now part of the standard library from Ruby version 1.9.
Bundler - Maintains a consistent environment for ruby applications. It tracks an application's code and the rubygems it needs to run, so that an application will always have the exact gems (and versions) that it needs to run.
RubyOnRails Framework - Home page of the RubyOnRails framework. API home page.
Rails Guides - Designed to make you immediately productive with Rails, and to help you understand how all of the pieces fit together.
The Rails 4 Way - (Book) The PowerRuby team has paged through this recently released book (early 2014) and believe it is very good for learning Rails and the technologies that surround it.
Rails Casts - (Fee) Once you've learned the basics of Rails you will want deeper topics and best practices. This site will save you a lot of time and is well worth the $9.
RubyOnRails Tutorial - Learn Web Development with Rails.
Agile Web Development with Rails - (Book) One of the leading books concerning RubyOnRails.
Code School - (Fee) Code School teaches web technologies in the comfort of your browser with video lessons, coding challenges, and screencasts.
Ruby Motion - RubyMotion is a revolutionary toolchain that lets you quickly develop and test native iOS and OS X applications for iPhone, iPad and Mac, all using the awesome Ruby language you know and love.
Ruboto - Ruboto is a framework and tool chain to developnative Android apps, using the Ruby language we all know and love.
It has been said by some in the Ruby community that a certification in the Ruby language isn't desired as much compared to a developer having displayed their work in public on sites like GitHub.com. Here is one of the Ruby certifications we know about: http://www.ruby.or.jp/en/certification/examination