Photography software in general.
Photo Mechanic, On1 plugins, and Capture One - there isn't a single piece of FOSS photography software that is remotely useful for my use cases.
High volume tethered shooting with automatic application of edits and adjustments in separate layers is basically impossible.
Fast culling of hundreds or thousands of images along with applying metadata with templates is also not really possible.
Darktable and Digikam are okay Lightroom replacements, but they don't come close to touching what is available in the proprietary world. Rawtherapee doesn't do tethering at all, and isn't very good at what it does do compared to On1 Photo Raw or Capture One.
a notebook and pencil in my shirt pocket are faster to open than a phone app
handwriting is faster than thumb typing
I can sketch an electrical diagram on paper way faster than anyone can with a stylus on some janky phone screen.
3.1) Even if there was a stylus/screen combination with the same haptics, fidelity, and input recognition speed as pencil on paper, it wouldn't be 0.78€
I can toss the notebook and diagrams to anyone working on a project with me with zero worry that they'll drop it, forget it, or look around in the rest of it
I can tear out a page and hand it to anyone instantly, instead of finding out what messaging app we have in common, copying (or screenshotting) the note and pasting it in an app
I can insert a note into a physical book, stick it to the inside of a toolbox lid, a wall next to an electrical junction, inside a breaker box, or any other surface, and always have location-aware reminders waiting for me when I need them.
With minimal environmental control, my notes are effectively immortal. I have notebooks of measurements and diagrams of most rooms, wall cavities, pipe runs, electrical runs, cable pulls, and dimensions of various equipment that have outlasted hard drives, backup tapes, and a few cloud storage companies.