Unlike the Galaxy S4 and other Samsung devices, the Nexus 7 doesn't have a Clear All option in the recent apps menu. It's a highly requested feature, as it cuts down the time required to go one-by-one swiping each individual app (you can't swipe away multiple ones at the same time).
Fortunately for us, there's now a mod that will add this feature to the Nexus 7, as well as enable two other quick ways to close all running apps. To start, you will need a rooted Nexus 7 (or other rooted Nexus device) with the Xposed Framework installed.
Install Recent App Cleaner
Recent App Cleaner... more