[1] Owner publishes Calendar on Office Online and Grants Access for Sharing
(which includes sending email to recipients)
Publish a calendar on Office Online
[2] Recipient adds published calendar.
Office 2007 & 2010 users will have a “Subscribe to this Calendar” or similar action button showing as part of the sharing invitation email from the publisher.
There appears to be no support for sharing in Office versions prior to Office 2007.