TENEX combined demand-paged virtual memory with an unusually humane interactive command environment, then became the basis of DEC's TOPS-20 and a major operating system of the early ARPANET.
J.C.R. Licklider's 1960 vision of man-computer symbiosis reframed computers from batch calculators into interactive partners for thought, helping define the research agenda that led to time-sharing, networking and personal computing.
Multics treated computing as a shared utility and introduced a cluster of ideas—hierarchical files, segmented virtual memory, dynamic linking, access control and online reconfiguration—that shaped later operating systems.
BASIC was designed at Dartmouth alongside time-sharing so that students outside specialist computing courses could sit at a terminal and write programs themselves.