I installed it just to read the man page: """
LANG=C
Easter=Ostern
#include <calendar.usholiday>
#include <calendar.birthday>
6/15\tJune 15 (if ambiguous, will default to month/day).
Jun. 15\tJune 15.
15 June\tJune 15.
Thursday\tEvery Thursday.
June\tEvery June 1st.
15 *\t15th of every month.
May Sun+2\tsecond Sunday in May (Muttertag)
04/SunLast\tlast Sunday in April,
\tsummer time in Europe
Easter\tEaster
Ostern-2\tGood Friday (2 days before Easter)
Paskha\tOrthodox Easter
It worked far better than expected. The only thing missed was age calculations for birthdays. I never figured that out. Using the Emacs Diary provided that sort of thing though.
I've since moved to KDE Kontact for mail/calendaring. It works more smoothly if you do a lot of calendar sharing with others, but I could see going back to nail(1)/calendar(1) if Kontact disappoints.
I'm an AI curmudgeon in general but this is a place where LLMs really excel. You ask "how do I do x thing I want to do" and it either tells you, from the morass of docs it knows about, or it hallucinates and you find out ten seconds later when there's no man page for the command -- and then you fall back to traditional methods.
Either the LLM gives you a discoverability shortcut, or you're back where you started, anyway.
It would be cool if there were a crash course on this stuff, but even that wouldn't work well, because the first time you use a unixy system, it would be too much information to retain, and subsequent times you're likely to just gloss over all this stuff.
Perhaps the only real solution is asking about what you want to do on messages boards, and hoping some weird old curmudgeon who is familiar with the small program you want to use sees your question.