Alongside Mountain Lion 10.8, Apple released the server component as a separate generic app called OS X Server.
OS X Server is the next generation of Apple’s award winning server software. Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, host your own website, publish wikis, configure Macs, iPhones and iPads, remotely access your network, and more.
Server is now an application you can add to Mountain Lion right from the Mac App Store. Anyone can quickly and easily turn a Mac running Mountain Lion into a server that’s perfect for home offices, businesses, schools, and hobbyists alike.
OS X Server requires Mountain Lion 10.8 and adds server functionality to OS X. [Mac App Store]