Cocos2d for iPhone is a framework for building 2D games, applications, presentations, demos, and more. It was originally made for Python and then ported to IPhone by Ricardo Quesada as an open source project with the MIT license.
This book will teach you the fundamentals of how to write games with this framework. As this book is meant to give you a basic knowledge of the most important aspects of Cocos2d, it will cover a lot of subjects very quickly. However, do not worry! Almost every chapter will include tasks for you to complete and examples for you to practice. Throughout this book, we'll make three different games and each chapter will build on the previous one, but can also be considered independently, so feel free to skip to any chapter that interests you.
Learning to use Cocos2d is really easy and will allow you to start building your games in no time. It includes a lot of sample code full of comments explaining every little part of it.
One of the greatest key points of this framework is its big, active community. Every time you get stuck with something or find some bug, you can pay a visit to their forum where a lot of great people will surely help you. You will also find a lot of useful tips and code to enhance your game.
Cocos2d follows the 'copyleft' idea, so when you start making your own modifications to any core part of the framework, you should send them so that they can be added to the framework. You are not obligated to do so, but if you do, you will help the community and the framework itself a lot.
As of this writing, Cocos2d for iPhone is in its 0.99.5 version. I have been using it from Version 0.7x and the improvements made by its author and the community have been huge. Right now, it is one of the most used 2D game frameworks available for iPhone development.
Cocos2d can be used to build any kind of 2D game; from simple puzzle games to intensive physics simulations. Right now, there are more than 2000 applications made with it. Among all those applications, there are some bestsellers such as Trainyard, Farmville, and Stick Wars.