Despite its extremely low price of $19.99, OS X Mountain Lion Server actually has a great array of features in five key categories: User and Device Management, Personal Information Services, Network File Sharing, Web Services, and Network Services.
User and Device Management
In order to manage users on your network, OS X Server has a number of built-in tools. Of course, there is a basic user manager to manage all of the accounts. You can also place your users into groups and assign privileges based on these groups. OS X Server also includes a utility called Profile Manager that allows you to configure Macs (10.7 or later) and iOS devices (iOS 4 or later) using almost any setting built into the machine (and more). For controlling older Macs, Open Directory and Workgroup Manager are also available.