Well, everybody knows that never such version existed , at least released to the public.
But what about a beta release? All we know that when a product reach the mass market, the engineers are working already in the next version. And that's what happened - at least in part - with the Classic Mac Os. According to some Apple engineers that worked in to this project, the new version had a new and advanced nanokernel with better memory management and multiprocessor support. The project was sadly cancelled by S Jobs because it could add more difficulties to the acceptance of the Next Step /Mac Os X. According to some sources, the project was named named Starlight ...