A free app for Android, by ManageEngine.

WiFi Analyzer and Surveyor is a free utility that can be used to monitor the WiFi networks available in your vicinity. It can help you identify the interference caused by other devices, and whether the network is fast or slow. This app’s monitor can find channel interference, weak signal strength, and slow networks for you. Also, you may search for all WiFi networks nearby using the app’s WiFi scanner. With the survey findings, you can also see the WiFi networks’ signal strengths. This one is definitely a must-have application especially when you need an internet connection. Simply install the app on your device and you may now start using the app.