Android Nougat: Google likes to play around with experimental features in Android betas. One such nixed feature is a powerful tool that lets you customise the little bar at the bottom of your screen with the Home and Back buttons. If you have a certain few Nexuses, you can get it back. The customisation tools break down into a couple of sub-features. The Clipboard feature allows you to drag items to the nav bar to save for later — for example, storing a bit of text you've selected. Another feature called Keycode allows you to save a series of keystrokes that you can activate at the touch of a single button later on. Think of them like rudimentary recordable Autohotkey scripts.
All of these features are pretty complicated and not intended for the average user, which is probably why they're not included in Android Nougat. However, if you have a Nexus 5X, 6 or 6P, you can flash the package from XDA below to get these features on your device. Note: This is all highly experimental, probably broken and not in any way sanctioned by Google. If you want to try it out, read all the instructions and proceed at your own risk.