Coca is a chainable, devise-based scheme for delegation of authentication. It works through a standard JSON API so the packet that you pass down on auth is completely configurable. See coca-rbac for a similarly transparent RBAC implementation.

Devise sets a "remember_token" cookie for Remember Me logins, but not for standard logins. This extension sets a separate cookie on login, which makes sharing login state between same-domain web applications easier.

Droom is nice and clean.