Web app plays music until you keep writing. When you stop, the music also stops.
Key features:
100% free. (limited number of texts you can save)
Pro, desktop version available.
It adds 100 music selections and unlimited saved papers.
It works with Word and Google Docs.
https://www.typeboost.io/apps
My comment: Wonderful utility does really boost writing productivity by interconnecting your ability to type continuously (or with brief pauses only) to the playback of the music style you have chosen. Highly recommended.
Try it out now: https://www.typeboost.io/