When I started working on Zen Wars I needed to pick a graphics engine I could use as UIKit’s performance was to weak for the game I was planning. I tested out Unity3D and Torque3D, but wasn’t happy as both didn’t allow you to natively code in objective-c well. I then stumbled on cocos2d, an open source objective-c graphics engine, designed for iOS.
While working on Zen Wars I contributed patches and enhancements to the cocos2d project when ever I stumbled across an issue or limitation as I consider it important to try and give back to open source projects if I benefit from them.
Project Page: Link