Minitube - Minitube is a YouTube desktop application.
NewPipe - NewPipe is a lightweight YouTube front-end for Android.
FreeTube - FreeTube is an open source desktop YouTube player built with privacy in mind.
LibreTube - An alternative frontend for YouTube, for Android.
VueTube - A simple FOSS video streaming client aimed to recreate ALL features from their respective apps (and more).
YouTube Vanced - Vanced is a modded version of YouTube with many features such as adblocking and background playback