Mac OS X Server
Mac OS X Server is a series of discontinued Unix-like server operating systems developed by Apple, based on macOS. It provided server functionality and system administration tools, and tools to manage both macOS-based computers and iOS-based devices, network services such as a mail transfer agent, AFP and SMB servers, an LDAP server, and a domain name server, as well as server applications including a Web server, database, and calendar server. Starting with OS X Lion, Apple stopped selling a standalone server operating system, instead releasing an add-on Server app marketed as OS X Server (and later macOS Server), which was sold through the Mac App Store.