In the past, if you wanted to develop IOS or Android apps, you needed to know different programming languages or frameworks. For instance, for IOS app development, you need to know Swift, which is written in Objective-C and is used to develop IOS apps or for Android app, and Java. More and more time is needed to develop IOS or Android apps. Fortunately, big companies like Facebook, Microsoft and Adobe Systems have recently released open-source cross-platform frameworks where you can develop IOS and Android apps. I am going to give more information about some of the latest technologies in app development.
For IOS applications, the output is an IPA file (IOS Application Archive), for Android Applications an APK file (Android package).