There have been several requests for a z-matrix editor over the years. We had something for v1.0, but never shipped it because it didn’t feel right. (Part of the problem is the need to renumber atoms to make a coherent z-matrix.)
I don’t have any code for using z-matrices in input generators (yet).
But there’s a working prototype that should be in the continuous / nightly build in about 2 hours. This should also make it more obvious that you can edit values in the property tables?
I also moved the code for updating the molecule geometry into a shared helper so it should be uniform to edit distances, angles, dihedrals, etc. between the bond-centric tool, the z-matrix editor, and the property tables.
I definitely need testers.
One comment from me – I’m just one anecdotal data point, but I personally had not knowingly heard the term Z-matrix before this discussion, whereas “internal coordinates” is terminology that I’ve understood since my undergraduate days. Calling the dialog/menu item that might make for better discoverability.
It’s tricky. There’s definitely a group looking for a “Z-matrix Editor” because it exists in Molden.
I’ll definitely think about the naming. Still trying to sort out the different formats because people will ask for the input generators too.
The third option I suppose is to use both and label it Z-Matrix (Internal Coordinates)
That’s going to make a very long menu item or window title… tooltip works though, as well as the headline of the documentation. 
For what it’s worth, I’m running a poll on BlueSky as well:
(Right now, it’s 9-6 in favor of “Z-Matrix Editor”)
Well, I think the word “Editor” could be dropped without issue.
First of all: Amazing to have this available. I need to work with z-matrices every now and then and every time I do, I struggle to recall the exact definitions and conventions and have to re-discover them via trial and error. Having this editor seems very helpful!
As for the naming, z-matrix is an actual named and recognized “file” format similar to XYZ files. See https://en.wikipedia.org/wiki/Z-matrix\_(chemistry)
Also, iirc there are a bunch of (subtly) different definitions for “internal coordinates” whereas at least I am only aware of one z-matrix format. So the name might be more “unique” in that sense.
However, I think we can elegantly get around this naming issue simply by cheating a bit: Just create two menu entries for the same editor. Name one “internal coordinates” and the other “z-matrix”. This would allow everyone to easily find what they are looking for and I think the UI cluttering caused by this is likely rather minimal.
