Ask HN: What's a web calendar that doesn't suck?

I'm looking to pivot from Google Calendar and FB Calendar to a FLOSS alternative that, to put it simply, doesn't suck. These are the features that matter most to me:

- multiuser support - public or private events - tags, or at the least, categorization by location - RSS/ATOM feed output (for all, or specific tags) - iCalendar / hCalendar output

Can anyone help me out here? Otherwise I'm thinking of just biting the bullet and making one from scratch in Arc Lisp, but if anyone has experience here it would be a huge lifesaver!

Disclaimer: this is for non-commercial purposes :-)