I created free tool longvacation.eu, first as something to try out new Copilot abilities. Later found out there are projects like holiday-optimizer.com that are solving similar issue, so I tried to differentiate.

Longvacation supports adding your partner calendar (just one for now, but I plan to add multiple in the future)

Longvacation contains multiple sources of holidays data and is extensible. Right now e.g. Spain goes deep as far as city level (for Barcelona and Madrid). Countries like India, Indonesia or Switzerland support regional holidays.

Shuffle mechanism - algorithm to place your days is non-deterministic so if you are not happy with the results, you can shuffle days around or add your personal constraints (Monthly caps, Never-vacation days, Locked vacation days (not touched by shuffle algorithm))

It's my first public project so I'm still learning how to promote it - currently I have around 3k visits monthly promoting it on X and LinkedIn

I recently open-sourced the code as well, so issues and bug reports are welcome :) https://github.com/Duzij/VacationOptimizer