It's a big day for Exchange users; one of the best Mac calendar applications, BusyCal, has just been updated to support Microsoft's enterprise collaboration technology. Version 2.5 is available in the Mac App Store now, as a free upgrade for existing users or US$29.99 for new licensees. The new version supports Office 365, full sharing privileges, public calendars, free / busy time, tasks and more. Of course, the new build is still compatible with both iCloud and Google Calendar hosted scheduling.
Mac users who work with Microsoft Exchange calendars may sometimes feel like they just have to make the best of a challenging situation. Microsoft's own Office client, Outlook 2011, works well, but doesn't necessarily deliver that "born on Mac" experience we crave; Apple's Calendar (formerly iCal) may feel right, but compatibility hiccups can drag down your calendar productivity. Even the popular Fantastical app relies on one of those full-featured calendars for syncing.
Back in the day, the original BusyCal application (up through version 1.6) worked with Sync Services and iCal / Calendar to deliver Exchange functionality to happy users. Unfortunately, as Apple's underlying synchronization technology was deprecated (not to mention being creaky and buggy for quite a while), BusyMac founders John Chaffee and Dave Riggle made the tough choice in BusyCal 2 to abandon Sync Services and restructure the app around the supportable cloud calendaring technologies. A number of features had to be left on the editing floor in that change, including publishing calendars local-to-Google and crossover LAN sync with cloud calendars. (I was personally irked about that shift, as I was apparently one of a small number of BusyCal 1.x customers successfully using the product to replicate my work Exchange calendar to a Google calendar so that my spouse would be able to track my comings and goings.)
Chaffee and Riggle have been working on Mac calendar apps for a long time; they were behind the remarkably capable Now Up-to-Date networked scheduling app that debuted on Mac OS 7 in the early 1990s. It's great to see their current product still evolving and responding to the needs of the Mac community. You can read more about BusyCal, and get a full rundown of using the app for sharing and collaboration, in the free BusyCal Take Control e-book by Joe Kissel.