A local piece of HTML works fine as a modern hypercard. Or various app platforms that give you a similar experience. As far as I can tell the pliability you want is already there.
This is honestly the weirdest and most wrong thing I've ever seen anyone say on HN. The two are not remotely comparable. Like, you no, you can't drag and drop to create a calculator with HTML.
I thought you were saying that making this work offline should be trivial. I didn't realize you wanted to replace the entire dev process, to have the end user make their own version from scratch.
So my reply was talking about the ease of installing a program that was developed like this but for offline use, not the ease of make-your-own.
You're of course right that making your own has no easy solution here. But that's a separate problem from working offline, and the way you talked about both problems at the same time confused me.
You can, however, have a single html document containing an editing environment that can be used to "drag-and-drop" together a calculator: https://beyondloom.com/decker/