Source : Free On-Line Dictionary of Computing

OpenStep
     
         An {object-oriented} {application
        programming interface} (API) derived from {NEXTSTEP} and
        proposed as an {open standard} by {NeXT} in 1994.
     
        OpenStep is the specification of the object kits of NEXTSTEP.
        OPENSTEP/Mach was an implementation of this specification.
        The original, OPENSTEP version 4.0, and really was NEXTSTEP 4.
        {Rhapsody} was the codename for {Apple}'s {Mac OS X} Server,
        which is really NEXTSTEP 5 (it calls itself "kernel 5.3" at
        boot time).
     
        OpenStep was designed to be implemented independently of the
        computer's operating system, hardware, and user interface.
        The {API} for {Rhapsody} will be a superset of {OpenStep}'s.
     
        When the OpenStep {API} is implemented for a specific platform
        and made into a product, it is written in uppercase,
        e.g. OPENSTEP Developer 4.2 for Mach, or OPENSTEP Enterprise
        for {Windows NT} and {Windows 95}.  Versions of OPENSTEP exist
        for Windows 95/NT, Solaris, HP/UX, and Mach.
     
        (1999-11-25)