Volume Power Tool

If your Android's power button is broken then this app is for you! Totally free,

With this really nifty app running on your Android, you can use the volume button instead of the power button to wake up your device!

IF YOU WANT TO UNINSTALL THIS APP go to Settings > Security > Device Administrators and remove the app from the device administrator list. Then you will be able to unable to install the app as you normally would.
If you are wondering why the app was on the administrator's list to begin with, it's because only apps that are device administrators can turn on and off the screen. You actually opted-in to this, but probably didn't bother to read the relevant messages when the app asked for this permission...

If this app is run without the screen off setting, then the long term behavior of this app becomes unpredictable, as it is subject to the operating system's whims to reclaim memory. We recommend that you enable the 'screen off in notification bar' feature if you plan to use the app for long periods of time.