Protube: App for listening youtube in the background
As said, an app to listen Youtube in the background. I found it useful to listen to stuff like German lessons when driving or walking around and another app is on the forefront. That is a pro feature that Youtube wants us to pay 9.99 per month. This app has it for 3.99 for life. I use this mainly for German lessons like "Learn German with Ania", and other ones that you could pass sometimes without actually seeing the video.
Interesting enough, the creator of ProTube is a German guy.
Edit: ...and removes all the ads that Youtube puts in their videos.