I'm looking for a calendar application, ideally one that can run on windows, Mac, and iOS. I want my data to be available offline, and -- here's the kicker -- I don't want to store my data on Google's servers, nor Microsoft's, nor Apple's. I want the data for the calendar to be stored locally, under my sole control.
I might then sync the data file myself using dropbox, spideroak, file transporter, or some other system. The point is I don't want my data
stored on someone else's servers. under someone else's control.