Drowser
Avoid rogue apps from running in the background with Drowser.
Drowser is a simple app that kills the apps you select when the screen turns off.
It requires root and uses it to kill the apps with an am force-stop <app-id>. This is a very impolite way of stopping apps. These might (and will probably) misbehave. You might also lose data because of this. Beware!
Download it
Donating
If you feel like donating, you can do so by using Liberapay 
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