Out of the millions of apps in the Apple App Store, only a few hundred have ever topped its free charts. Developers have learned the tricks to get there. Last summer, Bria Sullivan was getting ready to launch her app, an adorable companion called Focus Friend meant to help people manage their screen time. Her outlandish dream was to get 100,000 downloads. She’d been building the app with Hank Green, a... [10759 chars]