• Makes running your console, rake tasks and mostly everything else super-fast.
• Sort of like spork and zeus!
• Except better!
• Spork: Lots of awkward setup.
• Zeus: You need to run it.
• With Spring, all you have to do is use Rails' binstubs. Add ./bin to your $PATH. Beautiful.
• Bonus! No more bundle exec!

• New file config/secrets.yml for your sensitive data.
• By default it just contains Rails' own secret key, but you should put all your secret things in here.
• Presumably supposed to be secret... yet version controlled.
• As @espenhogbakk will tell you, version controlling your passwords is a bad thing.

- "Hey guys, we made this new file where you can put all your passwords instead of in config/application.rb!"
- "Awesome! Now we don't have to version control our passwords anymore!"
- "About that..."

• ... wat?

• Render different views or even behave differently for phones, tablets and desktop browsers!
• Awesome. No more hacks where you make a format called "iPhone". "iPhone" is not a format.
• Define variants in before actions (example in app/controllers/application_controller.rb).
• Use them in respond_to in controller actions (example in app/controllers/home_controller.rb).

• ActionMailer. Previews.
• Previews. For ActionMailer.
• Awesome.
• Sort of like LetterOpener and MailPreview.
• In fact, exactly like LetterOpener and MailPreview.
• Create previews in test/mailers/previews (example in test/mailers/previews/user_mailer_preview.rb).
• If you use rspec, you can customize where they live so you can put them in spec or whatever.
• Navigate to http://localhost:3000/rails/mailers/user_mailer to preview.

• Sort of like enumerize!
• In fact, exactly like enumerize!
• Except different.
• The good: Faster! Probably. It stores integers instead of strings. You won't notice.
• The bad: It's going to get ugly if you remove options.