I have made several small mobile apps. (http://anthonytietjen.blogspot.com/p/my-portfolio.html) I charge for some of them, but my White Screen Flashlight has ads. (https://play.google.com/store/apps/details?id=com.anthonytie...) If you are into programming, and are considering an app, make something super simple (like my Cost Per Sq Foot Calculator), and you might be surprised that people actually pay for it.