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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.
As a starting point, there are so many customized class specific character sheets (with form fillable pdfs) that better use the space than the traditional 5E sheet. I used these character sheets a bunch; I also used the earliest iteration of the MPMB sheet but haven't circled back to them in years. My "character sheet" has never been limited to a single double sided piece of paper. Since 4E, I've used a binder with a bunch of info broken out into chunks with dividers. I've kept multiple characters in the binder; several years into 5E, I noticed it was getting a bit full so finally chucked the 4E references still lingering in the back of the binder.