-
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.
Another tool worth mentioning is the Responsive Email CSS Inliner by HTML Email. Just like other conversion tools, this inliner works similarly by reading your embedded CSS in one window and making it inline in another. The feature that makes it stand out from the rest is that it also has a third window that demonstrates what the actual email would look like, both on mobile and desktop. Additionally, there is an option to download a .html file of the email. Since the tool is powered by Juice, an open-source project, it can also be easily integrated into your Node.js projects and works in client JavaScript.