I want to make two lists that anybody with the link(s) can add their name to (or strike it from). This has to work on all standard smartphones, and not require downloading an app.
Ideally, both lists would be viewable at the same time, but that is not a requirement.
(A two column table in Google Docs would have done the trick, except that it requires you to download the app to edit from your smartphone.)
A free alternative would be great, but I would prefer a modestly priced app ($25 or less for a week's use) over one with prominent ads.