FreeTube - FreeTube is an open source desktop YouTube player built with privacy in mind.
WebTube - Lightweight YouTube frontend
NewPipe - NewPipe is a lightweight YouTube front-end for Android.
Minimize play in background - This all-in-one application for android allows you to watch all videos while using a smartphone.
YouTube Vanced - Vanced is a modded version of YouTube with many features such as adblocking and background playback
8player Lite - 8player Lite lets you play movies and music from your phone or tablet on your Apple TV with features such as multiple library support, more file formats, subtitle support, and AirPlay.