App store (or app marketplace) is a type of digital distribution platform for mobile apps. Apps provide a specific set of functions which, by definition, do not include the running of the computer itself. Apps are designed to run on specific devices, and are written for a specific operating system (such as iOSx, Mac OSx, Windows, or Android). The functionality of complex software designed for use on a personal computer, for example, may have a related app designed for use on a mobile device. Such an app may offer similar, if limited, functionality compared to the complete software running on the computer. Apps optimize the appearance of displayed data, taking into consideration the device screen size and resolution. Besides providing continuity of functionality over two different types of devices, such apps may also be capable of a file synchronization between two dissimilar devices, even between two different operating system platforms. App Stores typically organize the apps they offer based on these considerations: the function(s) provided by the app (including games, multimedia or productivity), the device for which the app was designed, and the operating system on which the app will run.
App stores typically take the form of an online store, where users can browse through these different app categories, view information about each app (such as reviews or ratings), and acquire the app (including app purchase, if necessary – many apps are offered at no cost). The selected app is offered as an automatic download, after which the app installs. Some app stores may also include a system to automatically remove an installed program from devices under certain conditions, with the goal of protecting the user against malicious software.
Many app stores are curated by their owners, requiring that submissions of prospective apps go through an approval process. These apps are inspected for compliance with certain guidelines (such as those for quality control and censorship), including the requirement that a commission be collected on each sale of a paid app. With the ease of use apps offer, and their presence on most mobile devices, app stores rose in prominence in at the beginning of the 21st century with their adoption by the iOS and Android mobile operating systems. Similar systems for the distribution of apps written for other operating systems have also been available for some time (particularly Linux distributions since the early 1990s), through package management systems and their graphical front-ends.