Sling alternatives

YTMP : YouTube Music Player is the First and the Only YouTube Music Player that lets you play any youtube video as audio with tons of features such as Background play, Playlist merger, No Ads, and many more for free while saving up to 98% of your data.

Song Squad is a free music streaming app for IOS that allows users to create a library of unlimited playlists and songs for free. You can listen to any song that is on Youtube and it even plays in the background. You can also invite your friends to a Group Playlist where all the participants can edit the contents of that playlist in real time.

Simple VLC-based video player that can play multiple videos at the same time. You can play as many videos as you like, the only limit is your hardware. You can save information about the position, sound volume, loops, aspect ratio, etc in the playlist!