NewPipe - NewPipe is a lightweight YouTube front-end for Android.
Video Background Play Fix - Some sites may not work with Firefox for Android video background play feature.
YouTube Vanced - Vanced is a modded version of YouTube with many features such as adblocking and background playback
FreeTube - FreeTube is an open source desktop YouTube player built with privacy in mind.
LiteTube - LiteTube is an app that provides HQ video and audio streaming players.
LibreTube - An alternative frontend for YouTube, for Android.