Vinyl Music Player has a material design that is easy on the eyes.

It's easy to use and customizable (multiple themes including a dark one).

It supports folder browsing sleep timer and a tag editor.

Sourcecode: http://github.com/adrienpoupa/vinylmusicplayer

Licensed under GPLv3

Album cover: https://www.flickr.com/photos/vastateparksstaff/38645226714/ (CC BY 2.0)

Icon made by Nikita Golubev https://www.flaticon.com/authors/nikita-golubev from www.flaticon.com