Youlist solves a problem with youtube when wanting to create playlists with friends. It allows you to collaborate on playlists and create them together from youtube videos. I've used it myself to share interesting videos with friends without having to remember whether I received it on WhatsApp, facebook, Skype, slack or [insert other chat app here], it's all on my Youlist. I also use it for collaborating on music playlists together with friends, which youtube doesn't currently allow me to do.