An app store, also called an app marketplace or app catalog, is a type of digital distribution platform for computer software called applications, often in a mobile context. Apps provide a specific set of functions which, by definition, do not include the running of the computer itself. Complex software developed for personal computers may have a corresponding mobile app optimized for the device’s constraints. Today apps are normally designed to run on a specific mobile operating system—such as the contemporary iOS, iPadOS, Windows Phone, or Android—but in the past mobile carriers had their own portals for apps and related media content.