Apple's OS X 10.8 Mountain Lion Server is now available in the Mac App Store. With the package, admins can set up file server between Mac, iPads, and PCs, maintain a wiki server, manage multiple profiles, handle Time Machine backups, and sync calendars, contacts, and email for clients. While some familiar tools like Server Admin and Workgroup Manager are missing in this version, many of the features have been built into the Server app itself. At $19.99, adding the server doubles the price of the standalone Mountain Lion upgrade, but is considerably cheaper than the $49.99 Lion Server add-on. For a further look at what you can expect with the OS X Mountain Lion Server, feel free to peruse the Advanced Administration guide.
Update: This article previously stated that OS X 10.8 Mountain Lion Server was the first to launch as a separate app. We have verified that OS X 10.7 Lion Server was an add-on app as well and have changed the article accordingly.