Soye Player 2 is an extremely simple music player, originally developed for persons with limited cognitive abilities. It differs from most other players is that there are very few buttons to accidentally tap and do something wrong. You can start a song and stop it, nothing else. After the selected song has finished, it plays other songs in the your collection, album by album, and automatically stops after 4 hours.
There exists an even simpler version of this player in App Store, called Soye Player.