As opposed to Apple’s AppStore, 65% of the apps on the Android Market are free. So, where’s the trick ? Well, most of them show ads, you (the user) view those ads and when something interesting is shown you even click them. And that’s when the developer makes money. Sometimes $0.01 per click, sometimes $3.5 per click (at least that’s my record). Usually, those ads come from Google’s AdMob, Millennial Media or ZestAdz (there are more, but these are the largest three).