GFit by FutureGo is an android/ios app to read and control supported BLE treadmills - usually made in China but white-labelled and sold under different names. This is an effort to document the Bluetooth protocol for it, only for personal use.
Sold under brands - Fitkit, Cultsport, Voit.
Not in scope - Elliptical treadmill, Rowers (also supported by Gfit app, but not documented here)