There's Lightning calendar built into Thunderbird. https://www.thunderbird.net/en-US/calendar/
Other than that the options for alternatives are slim. https://alternativeto.net/software/lightning/?license=opensource&platform=windows
Sometimes I wish we could re-allocate half the dev hours poured in to the 10th txt/code editor, music player or terminal app in to this kind of thing.
+1 for Thunderbird for Windows, OSX and Linux..
I use OneCalendar, it works with a lot of email/calendar hosts, looks good, and is very responsive.
Alternatively, Thunderbird has a calendar feature built-in.
(Edit) failed to see which community this was, OneCalendar is sadly not open source.
Oh shit, I didn't realize they have a Windows app!
I've used it for years on Android, this is fantastic. Wish I could upvote you 10 times. I'd prefer open source, but this at least solves my problem.
Thunderbird is just, bad. It works, and is probably the least bad out there.
Edit: Shit, it's an MS Store app. Uggh. Hate that garbage.
Does it need to be a native app? There are good web calendars out there as part of things like Nextcloud, SoGo, etc..
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