To build the hardware side of the projects, you will need an Arduino board and some other electronic components.
To develop the Arduino firmware, you just need the Arduino IDE, which can be downloaded for free from the Arduino site.
To develop the iOS applications, you need the Xcode development environment (available for free from Apple). Since the Xcode is available only for the MAC platform, you need an Intel-based MAC computer. Most of the projects are based on Bluetooth 4 protocol. Hence, you need an iOS device that supports this protocol.
Everything is explained in detail in Chapter 1, Arduino and iOS – Platforms and Integration.