Test your apps in a variety of screen resolutions using a single device
Improve gaming performance by playing at lower resolutions
Material design interface
In-built profiles of popular devices; more can be added manually
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Requirements
Android Gingerbread or higher
Requires root in JellyBean 4.3 and higher
Overscan available only in JellyBean 4.3 and higher
Important Information
Some devices/ROMs are having reboot issues, a nandroid/Ti backup is recommended before trying the app.
If your screen becomes unusable after setting a resolution, wait for ~15 seconds. It should revert to your default resolution.
If that does not work, reboot -> wait for 2 min (for the service to start) -> reboot again -> wait for service to start.
Also please note that uninstalling the app won't restore default display settings. So please force stop the service first, if you want to uninstall. Also tell me why you uninstalled it. ;)