Double-tapping the Home button to call up the app switcher to jump to another app or close an app has probably become such a force of habit that you can't imagine app switching or app closing by any other means. But should you have an iPhone 6S or iPhone 6S Plus with 3D Touch and a desire to shun the Home button, there is another way to access the multitasking app switcher.
To open the app switcher with 3D Touch, press down on the left edge of the screen -- at the very left-most edge of the screen. Press down hard enough until the screen slides a bit to the right. From here, you have two options: quickly swipe right to jump to the last app you used, or slowly swipe right to open the app switcher.
And while we are on the topic of the app switcher, there is a setting that changes the way you swipe through the carousel of apps. Head to Settings > General > Accessibility > Reduce Motion and toggle the switch on.
With Reduce Motion turned on, swiping through the app switcher occurs in a more controlled manner. Apps are presented one by one, so you can swipe through the carousel more slowly but without ever skipping past an app you are searching for.
Check out each way to make your own decision about the Reduce Motion setting.
For more, see everything you can do with 3D Touch.