OPENSTEP is the version of NeXTis NEXTSTEP designed to run on non-NeXT hardware, specifically Intel-based hardware in this case. NEXTSTEP itself is the foundation for what became Mac OS X, which was acquired by Apple in the mid-1990s when Apple was looking for a way to replace what we now call Classic Mac OS.
OPENSTEP hasnit been updated in a number of years, but that didnit stop MacOnIntelis site admin, who writes under the name ppc_intel, from installing it on his Intel-powered MacBook Pro. He used a beta version of virtualization engine Parallels, and documented the experience with screen shots and photographs.
For those looking to get OPENSTEP running on their Intel-based Macs, thereis additional information in the comments for the article.