SoftKeyZ Root apk content rating is Everyone and can be downloaded and installed on android devices supporting 15 api and above.
"This application will let you change the Softkeys / Navigation Buttons fast and easily on your rooted Android device. This root app comes with more than 150+ different softkeys to choose from and the growing online database proivides even more user-submitted ones. If you got some navigation buttons you would like to see in this app just upload them to the gallery. Until I've added them, you can just use the import feature for these soft keys. This application needs root and "busybox" to be installed on non-nexus ROMs. This app will NOT overwrite your applied themes, or enable the navigation buttons on devices without them.
known problems: -Sometimes your wallpaper can reset itself. -The app is not compatible with most non-AOSP based ROMs -Especially not working on the LG G3/G2.
-works great on Nexus devices and most Motorola devices!
WARNING: This app modifies system files and should only be used with a flashable backup of your current ROM on your device. The developer is not responsible for any damages."