Rails 1.0
2005-12
	Ruby 1.8.6
Rails 1.2
2007-01
	REST routes
	respond_to/format
	ActiveSupport::Multibyte
Rails 2
2007-12
	RESTful routes improvements; nested routes
	/people/1/edit instead of /people/1;edit
	.html.erb instead of .rhtml
	t.type :name instead of t.column :name, :type
Rails 2.1
2008-05
	Time zones
	Gem dependencies (config.gem in environment.rb)
	named scopes
	record changes
	UTC-named migrations
Rails 2.2
2008-11
	Ruby 1.8.6, 1.8.7
	Internationalization framework
	Thread safety
	transactional migrations
	vendorized gems
	String#chars -> mb_chars
Rails 2.3
2009-03
	Ruby 1.8.6, 1.8.7, 1.9.1
	Engines
	use Rack middleware, Metal
	Nested forms
	dynamic & default scopes
*Rails 3.0
2010-08
	Ruby 1.8.6, 1.9.2, 1.9.3
	Merb integration
	ARel query engine
	new router
	new action mailer
	Bundler
	supports jQuery (not only prototype); Data Mapper (not only ActiveRecord) etc
Rails 3.1
2011-08
	asset pipeline
	HTTP streaming
	jQuery as default
	reversible migrations
	mountable engines
	mass-assignment protection
Rails 3.2
2012-01
	plugins deprecated
	faster dev mode
	explain queries
Rails 4.0
2013-06
	Ruby 1.9.3, 2.0
	strong parameters
	Turbolinks
	live streaming
	save for threaded servers
Rails 4.1
2014-04
	Ruby 1.9.3, 2.0, 2.1
	Spring preloader
	Variant templates
	Enums
	Mailer previews
	config/secrets.yml
Rails 4.2
2014-12
	Ruby 1.9.3, 2.0, 2.1, 2.2
	Active Job framework
	Adequate Record optimizations
	Web Console
	Foreign key support in migration DSL
Rails 5
2015-…
	Ruby 2.2.1
	rails command execute rake tasks too
	rake test TEST=… -> rails test …
	rake restart
	Rails API
	Turbolinks 3.0
	Action Cable (WebSockets; uses Redis)
	Model.where(…).or(Model.where(…))
	belongs_to required by default (=> optional: true)
	has_secure_token
	alias_method_chain deprecated (-> prepend)