Paste this into your site's Embed or HTML block (wedding sites, class pages, club and church sites). It shows this same live list: people can add to it and sign up right there, and changes sync both ways.
Anyone who can see your page can edit the list, the same as anyone with the link. Don't embed it anywhere you wouldn't share the link.
Anyone can start a list like this one. No signup and no app — you get a link you can send to whoever needs it.