OS 7 Concepts.
One of iOS’s most repeatedly used functions in day to day activity is its multi-tasking capabilities, via the app switcher. It’s accessed through a double click of the home button which slides the tray upward, giving you access to icons of your four last opened apps. It’s functional enough to get the task done while remaining unostentatious enough to not be a visual nuisance. Due to it encompassing a relatively sliver portion of the screen when activated, your thumb never needs to navigate too far from the original enabling point (the home button) to switch an app.