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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.
I use world anvil for the worldbuilding, to post summaries of the sessions, make a list of quests visible to my players and have articles about the player characters that the players themselves can edit too. This way they can browse through the lore and things they have done. For the actual session I have started using Diagrams.net that looks like this currently: Example It's low-res but it's in german anyway.
Session planning I use Home Brewery and write it like a published adventure from WoTC. The notes that go into writing that? Erm, no comment...(I’ve got more random word documents or pdfs on my laptop and pieces of paper all over my house than I would like to admit)