You're thinking of this [1]. Super duper cool idea, ahead of its time. Author seems to have transitioned to a ludicrous pricing model, but I suspect it's because the people who like it really _love_ it. I used to be among them, but then switched to org-mode .
It's all a matter of point of view I guess. Given that I replaced it with something costing zero dollars may explain my attitude. Also, the fact that it started out as basically free, and is now a recurrent expense over a hundred bucks a year.
That said, the author seems like a cool guy. Hope he's finding success.
Emacs org-mode -- it's less visually obvious that it's exactly equivalent from a structural / hierarchical point of view. But the editing experience is infinitely better, because Emacs.
Yes, Readwise was sort of an inspiration for me too, but looked like wasted potential as they don't track or use any algorithms for you to remember, and lack support for external links/sources (I may be wrong here).
[1] https://gingkowriter.com/