We recommend Ruby 1.9.3 for use with Rails. Rails 3.2 is the last one that supports Ruby 1.8. Ruby 1.8.6 and earlier are not supported, neither is version 1.9.1.

Source: Compile it yourself
Windows installer: Ruby, popular extensions, editor
OS X 10.5+: Included with developer tools
(then do "gem update rails")

RubyGems is the standard Ruby package manager. It's similar to apt-get, emerge, and other OS package managers. Download

With RubyGems loaded, you can install all of Rails and its dependencies through the command line:

gem install rails

New versions of Rails can be installed the same way.

Create your application skeleton and start the server:

rails new path/to/your/new/application
cd path/to/your/new/application
rails server

You're running Ruby on Rails! Follow the instructions on http://localhost:3000.

TextMate on OS X has long been the favored Rails editor, but the classic editors are still going strong. See VIM for Rails and Emacs for Rails. For a full-on IDE, check out RadRails, RubyMine, 3rd Rail, or Netbeans for Ruby.