[caspar]

As someone who suffered some severe mobility impairment a few years ago and relied extensively on eye tracking for just over a year, https://precisiongazemouse.org/ (Windows) and https://talonvoice.com/ (multiplatform) are great. In my experience the hardware is already surprisingly good, in that you get accuracy to within an inch or half an inch depending on your training. Rather, it's all about the UX wrapped around it, as a few other comments have raised.

IMO Talon wins* for that by supporting voice recognition and mouth noises (think lip popping), which are less fatiguing than one-eye blinks for common actions like clicking. The creator is active here sometimes.

(* An alternative is to roll your own sort of thing with https://github.com/dictation-toolbox/dragonfly and other tools as I did, but it's a lot more effort)