These steps must be followed in order to share your Calendar with Mac users using Outlook 2011.
In order to set sharing permissions for your Calendar go to Calendar > Folder > Calendar Properties.
Figure 1: Calendar Properties button
The Calendar Properties will appear, select the Permissions tab.
Figure 2: Calendar properties, permissions tab
To add a user and assign permissions click Add.
Here you are able to set very specific Permissions for each user you wish to have access to your Calendar. You are also able to Add-Remove user access from this screen.
You will be presented with the GAL (Global Address List).
Select the user you wish to grant access to and click Add.
Figure 3: Global Address List, Address Book
Click OK once you have selected the user you wish to grant access to.
In this example I will now assign Prospector Pete to have Publishing Editor over my Calendar.
NOTE: IF YOU SHARE YOUR CALENDAR WITH AN OUTLOOK 2011 MAC USER YOU MUST ASSIGN ATLEAST THE REVIEWER PERMISSION LEVEL
Figure 4: Assign permissions
By choosing the Publishing Editor option from the drop down menu you will see some items are automatically selected granting and restricting certain forms of access.
Figure 5: Review permissions
Please note: You do not have to use on of the pre-assigned permission levels; you may assign your own custom level of permissions using the check boxes provided.