Version 7
(V7) The unsupported release of Unix ancestral to all current commercial versions. Brian Kernighan announced the release of V7 in summer 1979, at the Unix User's Group meeting in Toronto.
Before the release of the POSIX/SVID standards, V7's features were often treated as a Unix portability baseline. Some old-timers impatient with commercialisation and kernel bloat still maintain that V7 was the Last True Unix.