Lot's of features given for being free. Marked as commercial since another app (Thank You) needed so as to not annoy you with "Please donate" messaged.
Works and looks fine, lacks attachment feature though.
Simple Calendar by Simple Mobile Tools runs on Android but not iPadOS.
Free version seems to be deprecated as of posting this ("No more updates"), well...
The free-as-in-freedom version continues to be available via F-Droid: https://f-droid.org/en/packages/com.simplemobiletools.calendar.pro/
Reply written about 19 hours ago
online/offline calendar with import export function
Our users have written 5 comments and reviews about Simple Calendar, and it has gotten 32 likes