Designer works great for GUIs with complex layouts. Having an intermediate XML representation puts a lot of distance between your code and your GUI. Sometimes this is good, other times is not. I rant a bit about this at the start of the introduction: https://guietta.readthedocs.io/en/latest/intro.html
One thing to add is a graph.
or were you thinking of something else?
There'a a gap a mile wide between
1) tools like Delphi, VisualBasic (the classic version, not .net), and to some extent, HyperCard
2) GUI builders, which were popularized by Visual C++
#1 doesn't have (visible) layers or abstractions. It's a different way to represent your program. You place a few controls, tie them to actions (code), and that's your system.
#2 is like onions, with lots of messy layers, and tend to be way more cumbersome to deal with than the code itself.
I don't know of modern-day graphical programming systems. I haven't kept up with Delphi, but people who have claim the last useful version is Version 7 from 2002. After that, it went through some messy transition.
That's the only thing I know that's really seamless like old times.
radio buttons still basically unsupported - no way of grouping them.
Add optional astropy units for values, maybe extending the tuple syntax: ('__a__', u.km). More difficult than it seems, because one needs to parse input strings. But very useful in a scientific environment.
'with' syntax still very limited, in particular locals() and globals() refer to the Gui class scope so for example anything imported at the beginning of the script is not available inside the with block.
Unit tests almost completely missing, also I have no idea how to properly test GUI code.
Meta-level: add this list to github :)