BusyCal iOS supports syncing with all the different types of accounts just as its macOS counterpart.

• BusyCal iOS can sync Events with its macOS counterpart through a cloud calendar server (e.g., iCloud, Google, Outlook, Office 365, Exchange, Fruux, Fastmail, or any other CalDAV server). Events added to iOS will sync → calendar server → BusyCal macOS and back.

• Tasks in BusyCal iOS sync with the built-in Reminders app or other services such as Todoist, Fastmail etc. If you have the same accounts set-up on the mac, BusyCal iOS will effectively sync with the mac app via these connections. Tasks added on iOS will sync → Reminders → BusyCal macOS and back.