Zoom is one of those UI controls, like the color picker, that has grown so familiar as to become almost invisible. Designers drag and drop it out of a mental library of stock functionality, and the most pressing consideration is whether to use a magnifying glass or a +/- button for the icon.
"Pinch to zoom" reinvented zoom for touch devices, and Apple made the gesture ubiquitous by including it in iOS. "Pinch to zoom" is now probably the single most broadly understood multitouch gesture; it feels like something we’ve been doing all our lives, even though it entered the popular lexicon barely six years ago.
Paper seems to be a favorite of Apple as well, winning both iPad App of the Year and Apple Design Awards in 2012. Apple also featured the app prominently on its home page as part of its 50 billion app download contest.