Devise: Flexible Authentication for Pragmatic Rails Developers
Devise (GitHub repo) is a new Rails authentication library/engine developed by Brazilian development company Plataforma. It's pitched as a "flexible authentication solution for Rails." Devise builds upon Warden, a general Rack authentication middleware, while offering Rails developers a flexible but easy to use front end.
Plataforma's blog post about Devise says that it's different to the incumbent libraries, Clearance and Authlogic, in that it provides a full stack solution like Clearance (unlike Authlogic) but allows you to use a custom model (not just "User") and gives you customized role support. It also has full i18n (internatiionalization) support out of the box and Plataforma has made available a complete demo app showing off how Devise can work within a small Rails app.
Devise is a full stack authentication system that provides 5 "strategies" out of the box. A strategy for authentication, one for "confirmations" (e-mails, etc), one for "recovering" accounts, one for "remembering" logins over time, and one to "validate" signups. You can, however, add your own strategies depending on what you need to do (they suggest a "invitations" strategy).