Devise

Devise is an authentication solution for Rails, built on Warden, a general Rack authentication framework. A model opts into Devise’s modules for sign-in, registration, confirmation, password recovery and account locking. Devise is a Rails engine, and its views are packaged inside the gem.

Devise supports ActiveRecord and Mongoid as its object-relational mappers. The extensions list is kept on the project wiki.

Worth knowing

The README says Devise requires a good understanding of the Rails framework, and recommends that someone building a first Rails application start with a simple authentication system written from scratch instead.