What is the programming language for XXX?
NeXTSTEP
NeXTSTEP (also stylized as NeXTstep, NeXTStep, and NEXTSTEP) is a combination of several parts: a Unix operating system based on the Mach kernel, plus source code from BSD Display PostScript and a proprietary windowing engine the Objective-C language and runtime an object-oriented (OO) application layer, including several ``kits'' development tools for the OO layers NeXTSTEP is notable for having been a preeminent implementation of the latter three items.