Calify allows you to open calendar files and event invitations in a variety of web calendars.

Double-click an *.ics file and see it open in, e.g. Google Calendar. Automagically.

version 1.0.0 for Windows 7/8/8.1/10
Multiple web calendars are supported, including Google Calendar, Calendar and Yahoo! Calendar.
Installation creates a system wide file association for iCalendar files (*.ics). Calify can also look for ticket listings for public events.
From The Blog
Introducing Calify
As a vivid user of Google Calendar, I have always lacked the ability to open event invitations or calendar files directly in Google Calendar.