App

An app, which is short for "application," is a type of software that can be installed and run on a computer, tablet, smartphone or other electronic devices. For instance, Microsoft Word is a word processing application. Someone broadly classified Apps into three types: native apps, hybrid and web apps.

Distribution

Biggest app stores are:

• Google Play - international online store developed by Google for Andoid devices
• App Store - Apple's App store for IOS and IPadOS.
• Microsoft Store - introduce by Microsoft for Windows platforms.
• Others:
  • Amazon Appstore - an alternative application store for the Android operating system.
  • BlackBerry World - the application store for BlackBerry 10 and BlackBerry OS devices.
  • Ovi (Nokia) for Nokia phones 
  • Windows Phone Store - introduced by Microsoft for its Windows Phone platforms.
  • Samsung Apps - introduced by Samsung .
  • The Electronic AppWrapper was the first electronic distribution service to provide encryption and purchasing electronically.
  • F-Droid — Free and open Source Android app repository.
  • Opera Mobile Store is a platform independent app store for iOS, Java, BlackBerry OS, Symbian, iOS, and Windows Mobile, and Android based mobile phones. 
  • There are many other independent app stores for Android devices.