Ruby on Rails 2.2 Release Notes

Rails 2.2 delivers a number of new and improved features. This list
covers the major upgrades, but doesn't include every little bug fix
and change. If you want to see everything, check out the list of
commits in the main Rails repository on GitHub.

Along with Rails, 2.2 marks the launch of the Ruby on Rails Guides,
the first results of the ongoing Rails Guides hackfest. This site will
deliver high-quality documentation of the major features of Rails.

http://guides.rubyonrails.org/2_2_release_notes.html