We had a project requirement recently that involved creating a public/group calendar in Microsoft Exchange that would be updated by various user personal calendars in real-time. After reviewing and trying a number of approaches and products, we implemented CodeTwo Exchange Sync. .
It enables automatic synchronization of data between Microsoft Exchange folders. It will also let you sync mobile devices with Public Folders on Exchange and any other non-default Outlook folders. The synchronized data can be of any type: mail, calendar, contacts, tasks, etc. It also has a filtering tool that you can configure to filter items before syncing or modify synced items on the fly.
We then set category color codes on the group/public calendar to make it easier to visually identify different user calendar items.