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n8n
Free and source-available fair-code licensed workflow automation tool. Easily automate tasks across different services.
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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.
This a good start. Sincerely, you have the scope and breadth nicely set. It has to be like this when you start a big project. If I was doing this project for a client who wants to build it mostly themselves, I would need to know even more and in specific how you intend to call you python pieces and gather them into the app. But assuming you have a method in mind (or are open to suggestions) then I would choose Bildr on the client side and Node-Red on the server and perhaps npn.io for some things. Happy to discuss further.