The Home Assistant team publishes the analytics they collect (for those that allow it). The integrations and add-ons pages might interest you if you haven't seen them.
Google calendar is a lot more popular than I assumed. I tried putting it on once but it looked like a pita so I just didn't bother. Maybe I should give it a real go
I currently have it watching my calendar and setting my alarms on my phone.
If I am on Early shift in my calendar it sets alarm for 5am, late shift, it checks if the kids are off school and if they aren't it sets my alarm for 7.30am.
If I'm on holiday and so are my kids, no alarms are set.
Damn, I guess I'm the only one with TasmoAdmin installed lol.
Edit: Is the Meteorologisk institutt (weather) integration really used by 77%? I read a couple HA weather threads and didn't see a single person saying they use it.
I thought the same thing about Met.no, but as it turns out I use that integration. I don't look at it ever, but it's there. I think I have one sensor thing that uses the forecast data from it.
I use it. Not only was it the default, but it was the only one I saw that didn't require a paid account with a weather service. What do you use for weather?