iCal de-dupe is an applescript that deletes duplicate events, often but not always caused by syncing iCal with Palm devices and other PDAs.
It examines each of your calendars in turn, looking for duplicated descriptions, start and end times and dates. If it finds two matching categories within the same calendar, it deletes one of them.
The script worked efficiently and happily on my MacBook Pro, scanning through a fair amount of data in 15 different calendars quickly.
One word of warning: it is not very communicative. There’s no confirmation screen or chance to double-check before deletion.
My first indication that it had finished its work was this dialog in iCal:
What were they? I’ll never know.
An AppleScript posted 
on macOSXHints late last year does the same thing.
De-dupe looks like it is freeware and is available from the developer’s web site .
[...] There is a simlar set of utilities of iCal that google:”ical duplicates” and Hawkwings.net [...]