I use Opensheet as the backend for storing reviews of my book. It's not CRUD, but easy enough to fetch data as JSON and display it on a website (and for free!).
x2, opensheet is one of those tools I use so often I forget how useful it is. It’s so nice to be able to take form responses (or just generic svg data) and display it to a user base without having to setup a SQLite database and APIs.
Highly recommended.
https://github.com/benborgers/opensheet