RestKit is an Objective-C framework for iOS that aims to make interacting with RESTful web services simple, fast and fun. It combines a clean, simple HTTP request/response API with a powerful object mapping system that reduces the amount of code you need to write to get stuff done.

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also links to a few other cheatsheets

better developing with Cocoa/XCode

The PyObjC project aims to provide a bridge between the Python and Objective-C programming languages. The bridge is intended to be fully bidirectional, allowing the Python programmer to take full advantage of the power provided by various Objective-C based toolkits and the Objective-C programmer transparent access to Python based functionality.

The most important usage of this is writing Cocoa GUI applications on Mac OS X in pure Python.