iCal

Calendaring on Mac has several options - iCal (Primary), Outlook & Thunderbird being among the strongest contenders.

Currently iCal is the best tool which comes bundled with OSX, just like Mail (for email) and works fabulously with both Microsoft Exchange & Google Calendar services.

Other than Microsoft and Google calendars, it also integrates with Yahoo! & CalDAV (protocol) calendar services.

If you are a corporate user and tend to interact with the Miscrosoft Outlook users, you may face a few challenges in sharing calendars using iCal.

iCal format does not play well especially with the Outlook Web users, since iCal is not recognized by the OWA (Outlook Web App) Browser Client.

References : The Best Calendar App for Mac

Credits : Image Concept of iCal Watch by Mac (Macoto) Funamuzu