As Chainfire describes the app, Recently aims to restore sanity, by limiting which apps are shown. In its most aggressive configuration, it will show you only apps that are actually running right now.
As you can see on the screenshot above, you can limit the apps by age and also by maximum number of apps listed in multitasking.
In its most aggresive configuration, there will be only running apps shown in multitasking.
What Recently does, is that it hides the other tabs and just doesn't show them in the list. Recently doesn't kill the apps. The app produces no wakelocks, only runs as a BG service.
Definitely a great idea, what do you think?
Lollipop & root access needed.