I've been using Google for the last decade and am owly moving away from it.

I'm on Fastmail (FM) right now. While I love their mailservice, the calendar and contacts integration is okey-ish, compared to Google.

Right now, my contacts are scattered across these services. New contacts that I add on my Android phone, are obviously not available on FM, and vice versa.

Therefore I'd like to setup a self hosted solution to manage contacts/calendars on a centralized place.

But right now, I can't seem to wrap my head around this topic. I often see caldav/cardav mentioned, but don't know how exactly they are related.

FYI: I'm a software developer, and I already host a bunch of services behind a reverse proxy.

Example scenarios:

• Install a full-featured calendar app (mobile, desktop, web) -> connect to my service
• Someone sends me a calendar invite to FM -> sync to my service
• I add a new contact on my Android phone -> sync to my service (make it visible in FM)
• I add a new contact in FM -> sync to my service
• I send a new calendar invite via FM -> sync to my service
• Bonus I send a new calendar invite via App, and it get's sent via FM to the recepients.

So my question is what self-hosted solutions (besides Nextclowd) are out there that would allow me to accomplish that?