From: DeskNow Knowledge Base

How to use DeskNow only as group calendar for an intranet
DeskNow version: 2.3 and later 
  1. run the Configuration Wizard, disable Instant Messaging, and choose to use DeskNow for internal mail only.
  2. login as admin
  3. go to Administration/Users and Communities
  4. click on Manage user classes
  5. click on the 'Normal' user class
  6. unselect all the options, except: "Use calendars", "Personal Calendar", "Edit preferences", "Change password", "Share  objects".

There is a default shared calendar, caled "Group Calendar". Users can post all common appointments there. Users also have a 'private' calendar, called "My Calendar", which they can share selectively with other users, following the normal operations (see online help).