Unix
Operating system from Bell Labs 1969 (Ken Thompson + Dennis Ritchie). Written in C (invented for Unix). Philosophy: small tools, do one job well, combine via pipes.
Direct descendants live today in Linux, macOS (BSD-based via NeXTSTEP), FreeBSD/OpenBSD/NetBSD, illumos (OpenSolaris). The POSIX standard (1988) abstracts the Unix API. "The Unix Philosophy" (Doug McIlroy) is the basis of modern devops mentality. Ken Thompson + Dennis Ritchie received the Turing Award in 1983. Bell Labs ended official Unix development — System V ended up at AT&T → SCO → IBM. Plan 9 (1992) was an experimental successor that never took off.