That person slumped over her cell phone is disengaged, isolated, lost in her own little world, right? Wrong, says SC Moatti. She's highly engaged - she's having a text conversation with a friend in Europe, playing a game with another, and looking for a good place to go to dinner with a third. Mobile technology has become such an integral part of how we interact that for many people, losing a cell phone is like losing a limb. And the most successful mobile apps are precisely those that enhance and multiply the frequency and power of our real-world interactions.

Moatti - a technologist and industry insider - says these kinds of mobile apps adhere to three universal principles: They must have a simple design, enable the user to personalize them, and be continually improved by their makers through relentless attention to analytics. She uses examples from a host of great mobile app creators - Facebook, Yelp, Lyft, Tinder, Aerbnb, Trulia, WhatsApp, and more - to demonstrate how it's done. Even as technology evolves and smartphones are replaced by smaller mobile devices such as watches and contact lenses, these three principles will remain evergreen. The market is full of how-to books for creating apps, but no works examine what qualities make for great mobile products. Until now.