Mac OS X is a line of graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers.
The server edition, Mac OS X Server, is architecturally very similar to its desktop counterpart but usually runs on Apple’s line of Macintosh server hardware. It includes workgroup management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others.
Apple also produces specialized versions of OS X for use on three of its consumer devices, the Apple TV, the iPhone and the iPod touch. The iPhone and the iPod touch versions of Mac OS are called iPhone OS. These variants of OS X only contain what is needed for their particular devices.