I think that would be Decker (https://internet-janitor.itch.io/decker). Not my project but I found it some time ago when I searched for Hypercard successors. The neat thing is that it works in the browser.
Why use it rather than Livecode (aside from the licensing of the latter) or Hypernext Studio?
Unlike LiveCode (or so far as I am aware HyperNext), Decker is free and open-source: https://github.com/JohnEarnest/Decker
HyperNext doesn't appear to be actively developed; the most recent updates I see are from last year, and it can't be used on modern computers. Decker's most recent release was yesterday morning.
I'd be happy to go into more detail if you like.
I guess I want a Flash replacement....