Genyoutube is an application with which you can explore the entire catalog of YouTube videos from your Android and download whichever ones you want to watch them offline.
Download videos from YouTube and watch them offline
You definitely won't find this application in Google Play. Nor this one nor any other that can be used to download videos from the popular online video platform. That's because they go against the policies of this online store, therefore, you'll only find its APK in places of the likes of Malavida.
The application works as a YouTube client that allows us to watch all the different contents hosted. Below each video there's a download button that saves the video on our device's internal memory, being able to choose between several different image qualities.
All in all, it's a simple application that's not too bad if you want to enjoy the best YouTube contents but without having to be online all the time. However, it could be improved as you're going to come across loads of ads.