Nearly five years after Apple launched the first appstore, the worldwide revenue for apps is expected to grow with 62% to 25 billion dollars this year. Both the Apple appstore and Google Play now offer more than 700,000 apps each. In early 2010, the Apple appstore offered around 140,000 apps. The Wall Street journal has a nice background article about apps in which it quotes from a Gartner research and some other sources.