Nothing Zimbra specific but you can use a general iCal widget like:
http://www.apple.com/downloads/dashb...calevents.html
Then just use the Zimbra REST URL for calendar.
Code:
https://SERVER/service/home/USER/calendar
Where USER is your Zimbra username, and SERVER is your Zimbra host. This URL is protected by basic auth so you may need to enter the username/pass in the url if this widget doesn't prompt for a basic auth. So in that case like:
Code:
https://USER:PASS@SERVER/service/home/USER/calendar