In addition to previous support for Google Calendars and iCloud calendaring, the BusyCal 2.5 update adds sharing with Exchange and Office 365. Exchange users can sync and share calendars as well as and schedule meetings.
Calendar Sharing — Each calendar can be shared with multiple users, each with different access privileges (free/busy, read-only, read/write, delegate, etc.).
Public Calendars — Company-wide public calendars can be subscribed to in BusyCal.
Free/Busy - Meeting organizers can view attendee availability when scheduling meetings.
Push — Changes are synced immediately between Exchange and BusyCal via Push.
I am a longtime owner of BusyCal and can say that the update to Version 2.5 went smoothly. A small setup assistant handled the configuration with an Exchange 365 account that I have for work. The software offers a number of nice little features that add to the Exchange compatibility such as graphics support and rich-text formatting in the Notes field.
The update is free to BusyCal 2.0 customers and $29.99 through the Mac App Store.
In BusyCal before Version 2.0, the software relied upon the Sync Services found in Mac OS X Snow Leopard and earlier. However, with the arrival of Mac OS X Lion, these Sync frameworks were depreciated and the iSync app removed. This change created issues for a number of programs, including Microsoft Outlook and Entourage. It meant that there was no longer reliable sync between Apple's Calendar and third-party calendars such as BusyCal, and disrupting sync with iOS devices that were synced locally through iTunes.
With Version 2.0 and higher, calendars are hosted with a cloud-based service, such as iCloud or Google Calendar. Local calendars can't be hosted on the local machine and published out to Google. Instead, users subscribe to remote calendars, either through iCloud, Google or now Exchange. With the update, I went through a somewhat involved process to get a calendar up on the remote service: export the events in a local calendar, delete it, and after creating a new calendar on Google, I flowed the old events into the now-subscribed calendar in BusyCal.
In a BusyCal support note on upgrading to Version 2.5, the company offers this advice:
You can still share local calendars on the LAN. But you can no longer republish cloud-based calendars (e.g. iCloud, Exchange or Google) on the LAN for others to subscribe to. Instead, you should host all of your calendars on iCloud, Exchange or Google, and have each computer sync directly with the cloud-based server.