Youtube Go is an official app from Google Inc. which is still in beta stage (Early access) and not yet available to download from google play store.
It is the most awaited application as this app allows you to download any youtube videos and saves them to your external SD card and can view them offline.
Youtube Go is not only limited to downloading videos as it also allows you to view, send or receive videos that were downloaded right from the application itself.
As Youtube Go is not yet available officially from Google play store, you can get the beta version of this app from apkmirror.
Download the .apk file transfer it to your android phone, install it and open the application.
Lightweight and Minimal
Youtube Go is light weight and its user interface is minimalistic. This in turn, consumes less memory and processing power and as a result, improves the user experience.
Play, Save, Send and Receive
Yes, You can do all of these at one place. YouTube Go allows you to play and save the videos without launching the official Youtube app. Addition to this you can even send and receive the videos which you have saved.