Comment by rwl
I have been working on implementing iCalendar/RFC5545 in Emacs Lisp. I recently submitted a large patch and hope it will be merged in the next couple of months:
https://mail.gnu.org/archive/html/bug-gnu-emacs/2025-11/msg0...
This will add an iCalendar library to GNU Emacs, allowing packages in core and third-party packages to work with the format. More on the decisions I made and what I learned here: