Xcode
Whether you’re a professional developer or just starting out, Xcode has everything you need to build your first iPhone app — and the best part is that it’s completely free.
With Xcode, you don’t need anything else to start developing apps for iPhone, Mac, Apple Watch, iPad, or even Apple TV. Once you learn how to develop apps, the sky’s the limit.
Xcode might be a bit hard to get the hang of it at first, but with the right book or tutorial, you can get started in no time.