Google's preview of Android N at I/O last week showed off a revamped app switcher interface. This has sparked some thoughtful discussion, particularly surrounding the inclusion of a "clear all" button. It seems obvious that app switcher interfaces are failing many of their users. Most people shouldn't have to be concerned with the distinction between open vs. suspended vs. purged apps, but that means they probably don't understand why their phones aren't operating properly after they repeatedly purge all. It's impossible to say whether Android's solution is a good one without knowing the technological implications of pushing the big red button (it's not actually big and red, but it sure seems like a kill switch). But we can ask what would make for a better app switcher in general.
The typical form of an app switcher is fixed by precedent: display apps in the reverse order that they've been used. Only after that do the real decisions get made, like whether only active applications are shown in the switcher. The answer is typically "yes" on the desktop, while on mobile, app switchers often scroll on and on to the beginning of time — apps last launched months ago. That made sense when the multitasking tray was first introduced in iOS 4. It was just a quick switcher; apps were being immediately killed when the home button was pressed, so every app in the tray had the same status.
With true multitasking that's not the case. Some tiles in the iOS switcher are "live" while others are "dead", purged to free resources. Even purged apps need to stay in the app switcher to stay eligible for background refresh, so removing an app that's no longer in RAM only does harm. But there's no reasoning with compulsive quitters; they'll swear they're doing good. It means that interface designers have to choose their battles. Android N's "clear all" button concedes that users want to see zero apps in their switcher, regardless of what that means to the operating system. It's a time-saver, eliminating flick after flick after flick.
Good app switcher design could benefit all users, saving time for quitters and providing useful information to power users. The iOS app switcher should only show apps that are suspended, still in RAM and ready for immediate reactivation. (This is similar to desktop app switchers, although there users decide when to quit apps, not the operating system.) This would limit the number of apps displayed to ten or so, but I frankly never look for an app farther back than three or four (Springboard or Spotlight are faster than hunting that far back in the app switcher). It's a simple solution that meets everyone's needs: power users can see exactly which apps are currently running and quit problem apps; most users will learn that the app switcher only shows "open" apps; and quitters will waste less of their time. Win, win, win.