.ICAL File Extension
What is an ICAL file?
Calendar file used by products that support the iCalendar file format standard; uses the same format as .ICS files, but uses the ".ical" extension, which is less common; used for sending online meeting requests and tasks.
The ".ical" file extension may not be associated with iCalendar files by default. However, you should be able to open them in any supporting iCalendar application, such as Apple iCal or Google Calendar.
NOTE: Apple iCal became Apple Calendar in 2012.