RestKit: It is a framework for consuming and modeling RESTful web resources on iOS and OS X.

AFNetworking: It is a delightful iOS and OS X networking framework.

MagicalRecord: It is a super-awesome, easy-fetching framework for Core Data.

Injective: It is the Cocoa/Cocoa Touch Dependency Injection framework with features for simpler TDD.

AGi18n: It easily localizes your iOS apps by automatically extracting texts from code and XIB files into localizable strings.

SDWebImage: It is an asynchronous image downloader with cache support with an UIImageView category (for ones not satisfied with UIImageView+AFNetworking functionality).

SSKeychain: It is a simple Cocoa wrapper for the keychain that works on Mac and iOS.

LUKeychainAccess: It is a wrapper for iOS keychain services that behaves just like NSUserDefaults.

FileMD5Hash: It is a library for computing MD5 hashes of files with small memory usage.

ISO8601DateFormatter: It is a Cocoa NSFormatter subclass to convert dates to and from ISO-8601-formatted strings. It supports calendar, week, and ordinal formats.

NSData+Base64: It is Base64 for NSData.

TransitionKit: It is a block-based State Machine API for Objective-C.

NSXtensions: It is a collection of useful categories for standard Cocoa classes.

BlockKit: It is a framework that block-ifies pieces of foundation and UIKit that are in desperate need.

Libextobjc: The extended Objective-C library extends the dynamism of the Objective-C programming language to support additional patterns present in other programming languages (including those that are not necessarily object-oriented).