There's no protocol for different calendar apps to send one another invites directly. They use email for that, which means they need an email integration. Email has the advantage of having been standardized back in the '80s and '90s, with only a few minor modifications since then (mostly for spam prevention). So different companies' email systems have to work together. Calendars just layer on top of that compatibility.

Stop thinking about what you want and think about what companies do for the answer.

You start a company to provide email service. You hire some developers and they craft the unique features for your email service. Once your email service is stable and secure, you don't just fire 9/10 of the staff and call it done? Email is enough for home users. But they don't like paying for email when every ISP out there gives it away for free. The bread and butter is business. They LOVE paying a small fee for every user. The size of that fee moves with services offered. All of a sudden, you're pushing your developers to offer Authentication, chat, calendar, file share, web serving, app development/hosting, directory services, video conferencing, VOIP phone service.

From a business standpoint, all these things things that seem like disparate services, tie together very well as you have entire teams that use the services in a coordinated fashion.

From your standpoint, you just want a calendar. But no one is going to pay someone to host a calendar for them. There's not enough signal intelligence in just a calendar to make selling your data worth it, so you have to choose from a package.

I recently tried to get away from outlook as my primary email / calendar. Tried a couple of different providers only to discover just how reliant I am on having seamless calendar invites.

Manually attaching .ICS files to email was not going to cut it. No matter how good caldav is for my phone to desktop, I need to easily make events / respond to them.

Probably because that's how most people know it from work. There it comes from Microsoft Exchange, Lotus Notes (I think) and Gmail.

Personally I have my calendars on my own Nextcloud instance. That's mainly for files. But I use that anyways, so getting calendars, contacts and passwords was a nice bonus.

Mainly because email is used so heavily for scheduling. For example, I emailed my tattoo artist back and forth a ton recently then they sent me a calendar invite that automatically got added for my shared calendar

The biggest reason they’ve been tightly coupled historically has been event notifications and invitations. It’s a lot easier for one email client to both create the event in the calendar, and send the event metadata (.ics file) to the invitees.

Nowadays, it’s honestly much simpler to have them entirely separate, at least for personal use. My partner and I use a shared NextCloud calendar which works well on both iOS and Android using CalDAV. Much simpler than Google/microsoft/icloud’s sharing options.

You say you just want a calendar, but how would you get the calendar entries? All self created? None coming in over email?

If yes, it sounds like you want a planner. You might have better luck looking up that as a keyword.

You can also host your own, check out radicale! Is quite simple.

You can just use the Calendar apps on your phone and/or laptop. Etar is a good option for Android.

If you want synchronisation, you will either have to set up a calDAV based server yourself, or use someone else's. I use Nextcloud, and it synchronises many things, like calendar, contacts, tasks etc., using DAV protocol.

There are some public Nextcloud servers with server-side encryption that you can go for. Setting up your Nextcloud just for calender would be overkill. You may want to take a look at some awesome-selfhosted list, if you are into self-hosting.

I'm not sure what you're looking for; I use mailfence and it is OK with the calendar but not great. I am able to avoid google that way, tho. I did have issues with folks who do use google, but I am willing to work around that. I pay something like US$5 per year.

Really can't tell you where it came from, but which part of the google calendar integration with gmail doesn't work for you? I'm quite happy with that.

But have a look at tweek.so, they are a calendar & task planner without email service, and free for personal use.

Hi, fruux.com is what you're looking for.

Most email services allow you to forward mail to other addresses, and download all your mail to move it to another provider.