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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
It also helps if authors have a Permission Statement or contact details on their profile. Here's a neat explanation of what that is by the person who runs the Blanket Permission Database, there's a really cool extension that highlights authors who are there so you can know without looking it up. (keep in mind that we manually add authors to this, so people not highlighted might have a statement, especially in smol fandoms. I sometimes try to go through the tags for my new baby fandoms to find new people, and hope that helps.)