Apple has just released iOS 5 Beta 5.
iOS 5 is a new iOS that will be released this fall. Beta’s have been released to registered iOS developers. You can join the iOS developer program for a reasonable price of $99 per year. Upon joining the iOS developer program, you gain access to helpful documentation, the newest version of Xcode and the iOS SDK, and, betas for builds of unreleased versions of iOS. Learn more about the iOS developer program at the official Apple developer website
And if you aren’t a registered developer for iOS, don’t try to put the newest beta on. Apple warns non-developers about trying to install the beta:
This version of iOS is intended only for installation on development devices registered with Apple’s Developer Program. Attempting to install this version of iOS in an unauthorized manner could put your device in an unusable state, which could necessitate an out of warranty repair.
Learn more about iOS 5 here