If you manage a WiFi network and you want to know exactly which devices are connected and what they're downloading, the application WiFiKill will allow you to know straight from your smartphone and tablet. Furthermore, it offers you all this information from a very user-friendly interface.
How to control the traffic of a WiFi network?
By installing this APK, you'll have access to a control panel that lists all the devices that make use of your network with their corresponding IP and name, as well as other details such as the manufacturer. You only need to run the app and configure your access point, for which purpose you'll obviously need your network access key.
From that moment onwards, any device that uses it to browse the Internet will appear on the list, regardless of whether it's an Android, a Windows PC, Linux, macOS, iPhone or iPad. You can check, without problems, what pages it visits and how much data it downloads.
Well, it's quite clear what you can use the application for: to spy on other people that use your same network. You'll probably find it very useful if you want to know what your kids are up to on their phone: you'll know even if they browse in incognito mode.
Free or Pro version? Which one shall I go for?
If something's for free and it works, just take it. The thing is that the free version, as well as showing adverts on the interface, disconnects every 5 minutes, so if we want to use it continuously we might be better off purchasing the full version via PayPal on the developer's website.
Another drawback is the fact that it won't work with unrooted devices. That means that you'll have to figure out how to root your device with some sort of app of the likes of KingoRoot to gain superuser permissions.