This one is recursive-grid for Hammerspoon users on macOS, and is probably the easiest of the open source implementations to fully customize. (I made it years ago)

...which supports Vimium-style hints mode as well as the grid-based approach shown in this "Mouseless (app) explained in 80 seconds" video. It also has a very responsive maintainer.

Personally I like vimium's approach much better than the grid. Unfortunately not everything has a good accessibility tree (Zed sadly doesn't), but I just realized loading neru's page that I'm behind in versions. I haven't tried the "Native Vision OCR" addition to hints mode yet.

I also like having a trackpad right on the keyboard (using a SoflePLUS2 right now though I'm not totally sold on column stagger). Then I can use a real pointing device with only a slight movement of one hand. In the Mouseless video, the creator has tried to minimize the distance by putting the mouse between the halves of his keyboard, but I think he's both compromised the keyboard position to ease using the mouse (arms wide and parallel with wrists turned inward rather than arms converging toward a more splayed keyboard with somewhat closer halves, untented to minimize vertical separation compared to the mouse) and might have an uncomfortably small mousepad to avoid doing this even more. Not a compromise I'd want to make.

Disclaimer: I'm one of the authors/maintainers.