Lark Player - Lark Player – YouTube Music & Free MP3 Top Player is a fine tool developed by Mobiuspace Tech Top Player.
FacePause - Look away to pause YouTube videos
Audiomack - The free SoundCloud alternative
CornerTube - Watch YouTube in picture-in-picture on iPad
Musicolet - Musicolet is a small yet feature-rich offline Music Player for Android.
Fenetre App - Picture in picture for your mac.