What is Devise in Rails?

Devise is the most popular authentication gem for Rails, providing a full authentication solution via a set of modular "modules". Core modules: :database_authenticatable (hashed passwords), :registerable (sign up/delete), :recoverable (password reset), :rememberable (remember me cookie), :validatable (email/password validations), :confirmable (email confirmation), :lockable (account locking after failed attempts), :trackable (sign-in stats). Devise generates controllers, views, routes, and migrations. Customize by generating Devise controllers and overriding methods.