OpenStep's an object-oriented application programming interface (API) specification for an object-oriented operating system that uses any modern operating system as its core, principally developed by NeXT with Sun Microsystems. OPENSTEP (all capitalized)'s a specific implementation of the OpenStep API, developed by NeXT. While originally built on a Mach-based Unix (such as the core of NEXTSTEP), versions of OPENSTEP were available for Solaris and Windows NT as well. The software libraries that s… (More on Openstep)