Thanks, guys. Both of these applications are really cool, but it's not fixing my problem. For example, my Personal calendar is showing up twice. I tested both of them, and Dupe Deleter found the same 11 duplicates in both, but it still treats them as 2 different calendars.
All calendars are listed under ICLOUD, except for one listed under SUBSCRIPTIONS. There are no calendars ON MY MAC (and I don't even see ON MY MAC listed).
Only one very old work calendar (from a previous employer) is not checked (but also appears as a duplicate calendar in these applications).
I sync my calendars to the cloud, I think. I haven't gone totally wireless, though, and still sync my iPhone with iTunes via USB cable. Again, they don't show up as duplicate calendars in iCal or on the phone, but show up as duplicates in both of these applications, and that may or may not be the reason that Siri is telling me that I have 2 haircut appointments this Saturday at the same time. 🙂