A mobile app is a software application designed to run on smartphones like an iPhone, BlackBerry, Android phone, or Windows Phone as well as tablet computers like the iPad or Galaxy Tab among other mobile devices. These mobile apps are usually distributed through an app store like the Apple App Store, Google Play, Windows Phone Store, or BlackBerry App World. Some of these apps are free, while others must be purchased. Mobile apps were originally developed for general productivity and information retrieval apps like email, calendar, contacts, stock market, and weather information. The increasing demand for smartphones and availability of developer tools, however, has lead to an explosion of demand for mobile apps, driving the rapid expansion of mobile apps into other categories like games, GPS, banking, ticketing, and so forth.