Clean master is a must have for your android device. The most great feature of this app is that it's a junk cleaner. When you install an android app, it creates some junk files that reside on your phone even if you delete that app. Clean master efficiently finds them and remove them permanently. This not only saves your smartphone storage but also makes it faster. 

This app also works as a task killer. You can also manage your apps(uninstalling, moving) using this software.

Clean Master is available for free in play store so give it a try and you will definitely like it.