Mac OS X Server is an App

The server-specific server applications and work group management and administration software tools from Mac OS X Server are now offered as “Server App,” an add-on package for OS X sold through the Mac App Store along with Server Admin Tools 10.7, available from the Apple support web site. There is no separate Server OS. This means that if you want server, you first install the Mountain Lion desktop release, a $19.99 upgrade to Lion, then separately download the Server App, also for $19.99. There is no separate server edition of Mountain Lion, just as there was no separate server edition of Lion. You cannot download the Mountain Lion Server App to a Mac that does not first have Mountain Lion installed.