ruby-lang.org is the main web site of Ruby. ruby-doc.com holds the docmentaiton of the Ruby programming language and its standard libraries.

Gems are 3rd-party libraries for Ruby. rubygems.org hold the information about them.

www.rubydoc.info holds documentation of Gems, the 3rd party Ruby libraries.

Learning Ruby

learnrubythehardway.org an online book to learn Ruby.

rubylearning.com

tryruby a web-based editor to try the basics of Ruby.

Screencasts

railscasts.com holds lot of screencasts about Ruby on Rails. Many can be watched free of charge. For some you need to pay. The production of new episodes has stopped in June 2013.

rubytapas.com a subscription only series of screencasts (2 every week) about programming in Ruby.

Web frameworks

Sinatra is a light-weight route-based web framework for Ruby.

Ruby on Rails

Ruby on Rails (aka ROR) is the most popular web framework for Ruby.

www.railstutorial.org is a tutorial for Ruby on Rails.

Ruby news

Ruby Weekly newsletter a weekly e-mail newsletter about Ruby.

rubyinside.com Ruby news on the web. (Stopped in October 2014.)

Other sites

apidock.com www.ruby-toolbox.com rvm.io www.relishapp.com bundler.io rubymonk.com www.railstips.org www.rubyflow.com practicingruby.com railsapps.org www.padrinorb.com rubykoans.com opalrb.org afreshcup.com www.hackety.com lotusrb.org pakyow.com ramaze.net rubyshow.com