Between the acquisition of NeXT by Apple in the late 90s, and the release of OS X, Apple tried and abandoned a path to merge the two company’s technologies into a new, modern OS. Ultimately, a similar but different path was chosen, where much of the proprietary technology that made OpenStep expensive (specifically Adobe-licensed PostScript) were re-created, and better compatibility (introducing Carbon into the Classic OS to give developers an easier migration path than the hard and fast change to Yellowbox) with existing Mac applications was provided for.
Nonetheless, what amounts to an experiment: Rhapsody, essentially the NeXTStep/OpenStep OS with Mac interface elements bolted onto it (sometimes), was incredibly interesting. Yellowbox was to represent the new app platform (with built-in multi-architecture support) while the Bluebox, for compatibility with Classic Mac apps was to be added before release.
Shortly I will outline instructions here for getting Rhapsody DR2 (x86) up and running in VMWare. OK, it turns out this process is exactly the same as for installing NextStep. In case it wasn’t obvious, these two OSes are very closely related.