I'm super impressed. I love the names (text not string) and extra fields (like the multiple choice and tensor). But I'm a bit concerned about the complexity. Don't answer these, I figured it out, but this is how it felt: how do I make an array (numbered list) vs a named list (object)? I didn't realize the intro document itself was, well, a document. I was thinking it was a typical website with a sidebar. Script, whiteboard, simulator (??) I though json was just a hierarchy. Schema, Interface, raw data, json. Its a lot of jargon. Is a document a type of json object? Is there a fundamental difference between whiteboard file and a document file? Is a whiteboard a type of document? Can a document be a field in a document? When editing an item, do I need to fill out the interface, methods, snapshot, etc. Where is the save/submit button? (I known their isn't one, but I kinda expect a "I'm adding a new field, okay I'm done adding it and want to go back to a table-of–contents view") I think the UI needs to answer these because it feels overwhelming). You probably even explain it in text somewhere, but let's be real; IRL people aren't going to read the docs.
Good news is, I think its easy fixes; hide the templates the first time someone is making something (only let them make a doc). Hide the methods, snapshots, etc too. Wait till they've done some stuff. Change the "x" button to "save" even though its not really saving.
The windowing system is really impressive, and I've always loved the detached tables of MacOS's spreadsheets. But at the moment I think it adds to the overwhelming feeling.
Don't let my criticisms weigh you down though! I would've been happy if this had 1/10th of the features.