morrowind OP , 9 months ago

That could work with any messaging service or app though. You just need some apis.

and all they have to do is update their contacts. People can use Hotmail or Gmail or Microsoft or self-hosted email, and integrate whatever calendar they like alongside it.

But well, that’s kinda the problem that spurred this question though, you can’t, because there are no independent calendar or email apps. If I use Gmail but want to dump Google calendar, too bad for me I guess.