I feel like we got a “true successor to HyperCard” 20 years ago, in the form of Lotus Notes. It was essentially “HyperCard decks shareable via email, with each deck backed by its own automatically-allocated Firebase-like document DB co-hosted on the author’s email server.”

(And, further, each email client had its own client cert, which it used for 1. code-signing decks it had authored, and 2. signing API requests to the DB server when the deck makes them. So every deck, and every request, would always have a “verified” email address associated with it.)

Essentially, it was the set of functionality provided by Google Sheets + Google Forms (and a bit more), without any web stuff being involved.

Obviously, it became a cesspit of badly-made, overly-interlinked Intranet apps, but this was more to do with the target market of non-IT enterprises—it was no different than what such organizations did with Excel.

I’d really love to see what a system very much similar to Lotus Notes, given a fresh coat of paint, and targeted to consumers, would be used for today. An app anyone could open up and make a little DB-backed interactive experience, then either push it to an in-app inbox of their friends [where it could then be re-shared further, virally] or onto a cloud service others could browse within the app.