The iPhone 6S has a gorgeous 4.7-inch screen, a super-fast processor, and arguably the best mobile camera on the market. But out of the box, it won't have the apps you can't live without. Finding a good mobile app is like discovering a best-kept secret: they can change how you work, take your email from nightmarish to manageable, and forever transform your mobile photography game. But the good apps are easy to find. It's the great ones you have to seek out.