Another pretty wonderful option, both for focus and for other uses of background sound is https://mynoise.net
It's very customizable at a level that most tools aren't, making it easy to (for example) pare back low bass or high treble if one or the other grates on your ears whilst working -- or amp up or down background conversation depending on your taste.
It's very customizable at a level that most tools aren't, making it easy to (for example) pare back low bass or high treble if one or the other grates on your ears whilst working -- or amp up or down background conversation depending on your taste.