In 2014 government regulatory agencies began trying to regulate and curate apps, particularly medical apps.
Some companies offer apps as an alternative method to deliver content with certain advantages over an official website.
User input allows for the users to manipulate a system, and device's output allows the system to indicate the effects of the users' manipulation.
Mobile UI design constraints include limited attention and form factors, such as a mobile device's screen size for a user's hand.
By Q2 2015, the Google Play and Apple stores alone generated billion.
Where the software does not allow this, some devices can be rooted to eliminate the undesired apps.