Cannie is a gem for authorization/permissions checking on per-controller/per-action basis.

A Twitter API gem with OAuth 2.0 authorization (not ready for production)

Simple authorization system for Rails applications. Allows you to develop applications with a mixed role based authorization and a context based authorization model. Does not supply authentication.

Trust is a resource oriented framework for authorization control. It is compatible with Rails 3 and 4. It has a loose coupling from the models, and features a native Ruby implementation language. Support for inheritance and namespaced models as well as nested routes. Even permissions scheme supp...

A portable, pluggable authentication and authorization service.

PickyGuard is an opinionated authorization library.

Contextually is a gem for running Rails controller tests under different user contexts in a convenient way. So you can test your authorization without much effort.

declarative_authorization is a Rails plugin for authorization based on readable authorization rules.

Signup or login using Paypal's Authorization or Permissions api's

Authlogic and Declarative Authorization Engine for Rails 3

JWT based authorization that includes current_user helper

Census uploads via csv files

Inferno Test Kit for the Da Vinci Prior Authorization Support IG

Rails authorization plugin

Simple object-based role authorization in Rails