Apple has recently announced the beta release of the 5th version of the iPhone SDK, which contains the framework, tools and compilers for making your own custom applications for Apple’s iPhone operating system. It provides also provides a simulator to run your apps on, which represents both the iPhone and the iPod touch. There doesn’t appear to be a lot of changes to this kit other than bringing it up to the latest OS version, but the download is free and there’s no sense working with the older version.

iPhone Developers