Domain/OS is the operating system used by the Apollo/Domain line of workstations manufactured by Apollo Computer, Inc. during the late 1980s, as the successor to the one previously used, AEGIS. It was one of the early distributed operating systems. Hewlett-Packard supported the operating system for a short time after they purchased Apollo, but they later ended the product line in favor of their HP-UX Unix variant. HP ended final support for Domain/OS on January 1, 2001.