As mentioned in the sidebar, this tool is inspired by https://shadows.brumm.af/

I've used it a lot, but it always lacked a few features I would've used extensively, such as shareable links, copying to Figma with a button click, ability to change the background color, and a library of ready-made shadows. Also, I think the terminology is perhaps a bit clearer for someone who hasn't looked deeply into how this layering technique works.