Free and no Ad. Supports and tested with Android 6.0 Marshmallow and Android 7.0 Nougat.
Your tethered device need built-in ability to enabled WiFi tethering. If your device WiFi tethering is locked by provider or implemented in nonstandard way this application will not work. You still can use this app on such device to switch WiFi tethering on other devices that have WiFi tethering.
* Before use Tethermote pair devices with Bluetooth and connect to WiFi tethering manually.
* If you have some powersaving system installed (some devices have it built-in) exclude this app from it.
There is Windows 10 app in the store with the same name to enable WiFi tethering on Android devices.
This application is Open Source project under MIT licence. Source code is available on GitHub by Developer Website link.