CocosBuilder is no longer maintained, but there is very happy news! SpriteBuilder is based on the CocosBuilder source code and well in the works towards a final 1.0 release. You can already download a preview version from SpriteBuilder.com or get the code from Github.
Testing your game on a mobile device has never been quicker or easier, just install CocosPlayer on your device (or in Simulator) and CocosBuilder will push your code over wifi in just a few seconds. Hit the publish button and your game will be saved instantly to a html5 web page. CocosBuilder has a rich set of functions, including boned animations, nestling of interface files, support for multiple resolutions and automatic scaling of your assets.