Spanning Sync
spanningsync.com
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Synchronize Google Calendar and Apple iCal. Share calendars between multiple Macs. Share calendars with your coworkers, family, and friends. And while you're at it, connect Google Calendar to your iPod, mobile phone, and other devices.