alt Hacker NewsYMMV and a lot of people hate it, but I've run Nextcloud for this for years. It has pretty comprehensive support for WebDAV and CalDAV. Has sharing and lots of different authentication options; I use OIDC with PocketID.
It used to be a constant headache to keep running, but ever since I switched to the TrueNAS/Docker plugin it has worked smoothly. I know a lot of other people also have had good luck with the much lighter Radicale if CalDAV is your primary concern.
> It used to be a constant headache to keep running
It’s been very easy to run for me since version 15 or something. Basically i just use the stock docker image and mount a few files over there. The data folders are bind-mounded directories.
As usual with anything php, it’s only a mess if you start managing php files and folders yourself. Php has a special capability of making these kind of things messy, i don’t know why.