Cocos2D is a free and open source framework for building 2D games on iOS and Mac OS X. Games can be created in Cocos2D in 30 minutes or less using nodes, sprites, actions and physics engines. Nodes form a parent-child hierarchy and sprites are subclasses of nodes that display images. Actions such as move, rotate and scale are used to animate nodes and sprites over time. Common game elements like the player plane, enemy planes, bullets and explosions can be created as nodes and sprites with actions to fly, shoot and explode. Touch handling and particle effects are also supported in Cocos2D for creating interactive 2D games quickly.