Recently discovered Datally: data saving app by Google that lets you set a daily data limit and other data saving features.
You can do some of this within Androids settings but the daily limit is a great feature to make sure you don't go over your data.
It has some other features as well that I haven't played with much.
Anyone else use this?
Not to be a jerk, I posted about it in Nov 2017
Ended up being of limited use for me personally but everyone's mileage will of course vary.