Domain/OS is the discontinued operating system used by the Apollo/Domain line of workstations manufactured by Apollo Computer. It was originally launched in 1981 as AEGIS, and was rebranded to Domain/OS in 1988 when Unix environments were added to the operating system. It is 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 HP-UX. HP ended final support for Domain/OS on January 1, 2001.