For calendar display, I'm very happy with FullCalendar (Perl module for output upcoming).

As for the calendar backend, I use a CalDAV server, in my case, DAViCal - it's not written in Perl but PHP, but I didn't have the need to write any PHP besides the configuration.

Accessing the server from Perl for creating the output for FullCalendar or maybe sending the reminder emails is easy using DAV::Cal to find the appropriate events and then take actions on it.