libCollections is an Objective-C library that brings methods from Smalltalk's collection protocol and Ruby's Enumerable mixin to Objective-C projects. libCollections adds these methods as categories to the Foundation framework's collections classes. (Not all of Ruby's Enumerable methods are implemented, but some of them aren't really relevant or useful and probably won't be.)

Enumerable is one of those things that is hard to live without once you experience it. Great additions to Foundation.