NewPipe

NewPipe is a Youtube client that doesn't use any libraries that are dependent on Google's framework or on any Youtube API. The application is limited to analyzing Youtube itself in order to obtain needed information. This basically means that you can use this app on ANY device, even the ones that don't have Google Services installed.

The best part about NewPipe, however, isn't being able to use it without Google Services: it's everything else. Like its small size (barely 2 megabytes) and other features, like the possibility of listening to videos while they play in the background, or even downloading them. In fact, you can either download the video or just the audio.

In NewPipe's configuration options, you can choose your preferred resolution (360p by default). You can also link up an external video or audio player in order to play your videos. And, of course, you can choose the directory where you want to save all of your downloaded video and audio files. Another really interesting option lets you force all the traffic through Tor.

NewPipe is an outstanding YouTube client that lets you download Youtube videos with total privacy. The best part is that it lets you stream music in the background and do practically anything you can do with the official client.