TripMode for Mac
MacBook users know how useful it can be to tether to a hotspot (like an iPhone or cellular-capable iPad) from time to time. Unfortunately, this can result in accidentally burning through your monthly data allowance because you left your cloud backup on or whatever else.
TripMode is an indispensable Mac app that automatically reduces your mobile data consumption when you use a mobile hotspot. When enabled, it prevents all your apps, software updates, online backups, and photo syncs from accessing the internet, except for those you've whitelisted yourself. It also lets you track the data usage of individual apps so you can track down the data-hungry ones and put a stop to them.
You can't find Tripmode on the Mac App Store as of this writing (February 3rd, 2016) because Apple doesn't allow apps with Kernel Extensions. For now, that means buying it for $7 at the TripMode website.