Isn’t that Paul Atreides?

Nah, this is probably more related to fact that a bunch of people burnt a book or twelve.

Ok, so this is a ”how many colors of the rainbow there are”

If you go balls to the wall, all out retardation: Nextcloud, the CalDAV is basically just a bonus, I’ve replaced google.com at home with Nextcloud

Some middle ground: SoGo, sogo.nu

If you just want to solve this specific problem: Radicale, https://radicale.org and Baikal, https://sabre.io/baikal/