I really like the UI especially the about page. I don't think you are supposed to be able to see the about page on the playing page (it took a bit to start and then started when I was in about) but it looks good there with the blur.

Here's a list of other sound/relaxation websites: https://fmhy.net/audio#ambient-relaxation.

This one is pretty funny but not relaxing to me. It may be a covid remnant: https://imisstheoffice.eu/