Android N Revamps the Multi-Tasking Button: Double tap to Switch to Recent App, Long-Press to Split-Screen

A staple of Android custom ROMs is finally headed to stock Android builds: the ability to switch to the most recent app by double tapping on the recents button. In addition, long-pressing the recents button will turn the icon into a split-screen button, allowing you to quickly enable multi-window with the most recent apps you have used.

source: xdadevelopers