CTSS is kind of the great-grand-daddy of operating systems. As well as influencing Unix (via Multics), it also had a lot of influence on DEC operating systems and IBM mainframe operating systems (in particular CP/CMS which evolved into VM/CMS and now z/VM). You can even trace Windows as having ancestry from CTSS via multiple historical paths (CTSS -> Multics -> Unix -> Xenix -> DOS 2.0 -> Windows; CTSS -> CP/CMS -> CP/M -> DOS 1.0 -> DOS 2.0 -> Windows; there's probably even some CTSS heritage in VMS and VMS in-turn influenced Windows NT)
