iCal4j - FreeBusy
The iCal4j FreeBusy service provides support for generating iCalendar free/busy information from existing iCalendar data.
Overview
The iCalendar specification defines the VFREEBUSY
component that may be used to request, respond or publish
resource availability.
Command Line Usage
Query for free one hour slots
ical4j-freebusy/bin/ical4j-freebusy request -F ./Australian32Holidays.ics
Result: