Interop - Are you free or busy?
While we'd love the whole world to instantly convert to Zimbra, we realize that from time to time people have that one department or peer organization running a different system.
To solve that it's time to announce our Free-Busy Interop is now out of beta - we're hereby officially supporting two-way free/busy information, schedules, and global address book access with Microsoft's Exchange Server, IBM's Lotus Domino Messaging Server, Meeting Maker, and a slew of other third-parties that interact with our free-busy API framework.
The query and propagation extension of free/busy data is done via REST and WebDAV interfaces. If you need more info on how to set it up checkout SRC/ZimbraServer/docs/freebusy-interop.txt (you can grab a copy via perforce / this post) or ask us in the ZCS forum section.
Kinda related: Don't forget that Zimbra side you can now visit http:// server.domain.com/home/username?fmt=freebusy to display an aggregate HTML calendar of the user's free-busy data. (Of course you can always choose to select "exclude this calendar when reporting free/busy times" if you wish.)