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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.
MaxGraph (fork of MxGraph)
You could also directly use libraries like Raphael or D3(lots of the tools around use D3.js as their core rendering library) if you just want help with drawing the SVG elements and connectors ... that is, if you're going to pull the data from the DB, decide in your app what each shape should be and where it should be on the page, etc. Integrating and driving these directly from Angular isn't trivial, but there are books and blogs to help (for example, see https://edupala.com/how-to-use-angular-d3js-chart/)