Everything is stored and synced locally only on your device. Very Good Calendar Sync never transmits or saves your calendar data externally.
Google Calendar, Microsoft 365, Apple iCloud, CalDAV and others. If it shows up in macOS' Calendar.app, it works with Very Good Calendar Sync.
Synchronisation happens locally on your Mac, so it only runs while your Mac is awake and the app is active in the menu bar. Enable "Start at Login" in Settings and it will start automatically whenever you log in, so you never have to think about it.
Not yet. Very Good Calendar Sync is focused on a native macOS experience to start with. Windows support is on the roadmap, but no timing on that is available at this point.
Unfortunately, no, because iOS doesn't support the necessary features to make it viable. Most notably, the lack of background processing based on calendar notifications.
At the time of writing, there's no guaranteed way to make it work based on the rules of what apps are allowed to do when running in the background. This makes it too unreliable. Always having to open the app to manually trigger synchronisations goes against the core idea of not having to think about the synchronisations in the first place.
Until there's better support in iOS, there is no way to make it work seamlessly.
Your first synchronisation is completely free with no time limit. When you want to add more synchronisations, you can pick a Monthly, Annual or Lifetime plan. All plans include a free trial. See the Pricing & Licensing page for details.
Your extra synchronisations are paused, not deleted. The oldest synchronisation stays active under the free tier, and all paused synchronisations will resume as soon as you reactivate a plan.
Yes. All plans are per-user licenses, so you can use Very Good Calendar Sync on all your Macs with the same Apple Account.
However, avoid setting up the same synchronisation on more than one Mac. Because synchronisation data is stored locally, each Mac works independently. If two Macs synchronise the same source and target calendar, you will end up with duplicate events in the target calendar.
Very Good Calendar Sync