Can I run apps in a smaller resolution? I have a Samsung Galaxy Tab 4 (SM-T235) tablet running Android version 4.4.2. It is 7 inch, which is nice, but sometimes (for example, when walking) I would like to be able to hold my device in one hand and only use my thumb to interact with the app that I am using. Perhaps even change the resolution so that is like a regular mobile device.

Basically I would like to have a way to run apps in a smaller resolution and have it not scaled to fit the display so that I can reach everything with my thumb using only one hand.

See the image below for an example that i have in mind.

I have complete root access and am a developer (I don't really need 'simplified' answers, give me the tech details!)
You can run su wm overscan LEFT,TOP,RIGHT,BOTTOM from Terminal (Superuser privileges needed)  

If you do not have Superuser privileges, you can hook your phone to a PC and run ADB command
adb shell wm overscan 200,200,0,0

For example, to achieve what you've shown in the picture above try running
wm overscan 200,200,0,0.  

But I must warn you, before running that, be sure you have USB debugging switched ON just in case overscan messes up your display, you can run
adb shell wm overscan reset from the PC connected.

WindowManager (wm) commands work on devices running Android 4.3 and above

May require a Reboot to achieve proper re-size.



Alternatively you can use Niwatori module if you have Xposed framework on your device.