A Little Ruby, A Lot of Objects (Brian Marick)
The goal of this book is to teach you a way to think about computation, to show you how far you can take a simple idea: that all computation consists of sending messages to objects. Prerequisites is reader will know at least one programming language, not necessarily.
Author(s): Brian Marick
NA Pages 
This page covers the following topics related to Ruby : The Fundamentals, Installation, Tweet Fetching, Style, Conventions, and Debugging, Numbers, Strings, Variables, Methods, RubyGems, If and Else, Loops, Collections, Enumerables, File input/output, Reviewing Tweet Fetching, Supplementals, Design and Theory, The Projects.
Author(s): ruby.bastardsbook.com
NA Pages
Ruby Programming by Wikibooks.org
This book is currently broken down into several sections and is intended to be read sequentially. Topics covered includes: Notation conventions, Basic Ruby, Ruby Semantic reference, Built in Classes, Standard Library.
Author(s): Wikibooks.org
NA Pages
