Mac OS 10.5/10.6 iPhone SDK (Software Development Kit 3.0/4.0).

IPhone SDK consists of:

IDE to develop iPhone Apps is XCode(This tool is inbuilt in iPhone SDK)

Interface Builder This is used to design GUI of Apps(Inbuilt feature of iPhone SDK)

Instruments This is used to check any memory leaks in our apps (Inbuilt in SDK)

Simulator This is used to test our apps before deploying into real device.