App ranking algorithms determine how mobile applications are ranked on app stores. Each app store - eg, Apple’s App Store and Android Apps on Google Play - has his own algorithm but operating principles are quite similar.
App ranking algorithms are usually based on downloading numbers, downloading acceleration and user ratings.
Mobile marketing vendors offer app publishers to influence or "manipulate" rankings and algorithms by promoting apps through "free app of the day" models. Some of these dedicated services have seen their apps banned from App Store for violating app developer T&Cs.