Note: the App Store links no longer work as I have quit iOS development. However, I am working to get Bluetooth Serial and Bluetooth Serial Pro back on the App Store through someone else's developer account.
Eaze is a free and open source Cleanflight Configurator for iOS. It allows you to set up and tune your flight controller wirelessly using the cheap HM10 BLE module. Source code is available on GitHub, and here is a tutorial on using Eaze.