CanCan
Authorization Gem for Ruby on Rails
...It centralizes all authorization logic in a single Ability class, where you define what actions each type of user can or cannot perform on different resources. Developers then use helpers like authorize! in controllers or can? in views to enforce those rules without scattering permission logic across the application. It supports defining permissions using conditions, allowing granular access based on attributes like ownership or role. Because it abstracts authorization cleanly, applications stay easier to read, test, and maintain as business rules evolve. Though no longer actively maintained in its original form, CanCan inspired forks and successors (such as CanCanCan) that continue to be widely used in Rails projects.