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proelements
This plugin enables GPL features of Elementor Pro: widgets, theme builder, dynamic colors and content, forms & popup builder, and more.
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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.
Its under the GNU General Public License and has a github. Additionally, Elementor has large developer support to the community, with huge variety of free and paid plugins out there that extends its support. I am not a lawyer, but nothing is stopping developers on making their own plugins that extends the support on Elementor. This is just one of them that emulates the same things Elementor pro has.