Already last year I encountered the great http://worrydream.com/LearnableProgramming/ and it was much needed fresh air (while I was suffocating in my provided "textbooks": cobbled collections of random things difficult to follow). But for some reason I didn't appreciate it fully. I read it again now and, wow, it's so wonderful that I can't really express how I appreciate this thorough and lucid thought style.
Well my point is now a bit more mundane. The examples in the essay look very real, but I couldn't find any reference to the tool used, I only understood (from different sources) that it's Bret's own creation. I would like to use it directly or as a starting point for further work as it looks so well done and it is a lot of work. It would without doubt benefit the students infinitely. I would even pay for it.
I found choc: https://www.newline.co/choc. But it seems to be partial and missing at least the abstraction of vars and functions (see the essay).
Anyway, just to be clear and explicit: thanks a lot to Bret for making what is arguably the best tool for computer science teaching I have ever seen, going really to the fundamental needs of students.