Comment by RiverCrochet

One cool thing Microsoft did with Windows NT was the whole local security model and a filesystem that supported them (NTFS), which was definitely richer than UNIX. I don't really know if other UNIXes at the time had anything more than the 16-bit uid and gid and mode bits on everything the filesystem. I wonder how it would have looked if Microsoft kept Xenix as the base and added ACLs on top of it, for example.