What do you know about your mobile app users?
Average number of installed apps on smartphone, number of actively used (last 30 days) and number of paid apps in Australia, according to Google's Our Mobile Planet
Number of apps available in App Stores. According to Statista as of July 2014
Most popular Apple App Store Categories as of January 2015
Time spent per month according to Nielsen
About code re-use and inventing wheel in 2015.