In iOS: Can my app launch another app and get a response/acknowledgement back?
Custom URL Schemes
You can define and use a custom URL scheme to interact with other apps on iOS:
Defining a Custom URL Scheme for Your App 

Custom URL schemes provide a way to reference resources inside your app. Users tapping a custom URL in an email, for example, launch your app in a specified context. Other apps can also trigger your app to launch with specific context data; for example, a photo library app might display a specified image.