Niwatori was a module that created by tkgktyk, which supports up to Android 6.0 (marshmallow). This one is a reborn package that you can find the same experience and some other awesome new features. It supports back to Marshmallow and forward to Oreo.

Be Noted:
I only tested on some OnePlus phones and Pixel(Nexus) phones. I don't promise it works on every Android device. Please submit an issue on GitHub page and attach Xposed logs if you find it crashes on your phone.

Features:
- 3 types of One-Handed modes:
* Small Screen
* Moveable Screen
* Slide Down
- Gesture triggering: swipe on screen left/right edge to trigger small screen mode.
- Outside gesture support on small screen (touch outside content to manipulate the shrunk screen)
* slide down the shrunk screen (this is very useful to me)
* scroll left/right to zoom out/in the shrunk screen (biggest ratio is 90% and smallest is 40%)
* single tap to reset
* double tap to swap left/right
* All the gestures are configurable
- Double tap on shade area at the bottom notification panel can shrink notification panel and you can manipulate the small screen with all the gestures.
- Configurable persistent small screen or auto reset while activity switching.
- A lot of configurations that make your outstanding one-handed smart phone.

GitHub page: https://github.com/zhougy0717/Niwatori
XDA thread: https://forum.xda-developers.com/xposed/modules/mod-niwatori-one-handed-mode-t3730963
Recommended as a replacement for XDA One-Handed app: https://www.xda-developers.com/one-hand-mode-niwatori-xposed-module/