xDrip is an open source Android app.
It was created years ago by a diabetic who was not happy with the available apps for monitoring her blood glucose.
It has been continuously enhanced over the years.
It is maintained by volunteers.
xDrip is not FDA approved. If you choose to use it, you can. But, it will be your responsibility.
The xDrip developers earn no financial, or indirect, benefits if you choose to use it.