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.