Pull To Refresh - available in iOS 6.

UIViewController Containment APIs. iOS 5.

Custom Tab Bar. iOS 5

Custom Navigation bar. iOS 5

HTML Strings. iOS 7

@2x only. iOS 7

Flat out. iOS 7

viewDidUnload. iOS 6

AutoLayout. iOS 6

UIDynamics. iOS 7

Receding keyboard like the messages app. iOS 7