Let's start here, This is the Current Market Share of all Operating Systems from end user devices using the internet

http://gs.statcounter.com/os-market-share

Then let's ask "What is the Android OS built on?

Linux

What about iOS?

Unix

That is 60%, but it does not stop there, those are just clients

38.90

14.97

8.07

0.89

62.83

What Is The Most Used OS In The World ?