[TUHS] First Unix-like OSes not derived from AT&T code?

[Andrew Warkentin]

What was the first "clone" functional Unix (i.e. an OS not derived
from genetic Unix code but highly compatible with genetic Unix)? Idris
is the earliest such OS of which I am aware (at least AFAIK it's not a
genetic Unix), but was it actually the first? Similarly, which was the
first "outer Unix-like" system (i.e. one with strong Unix influence
but significantly incompatible with functional Unix)? Off the top of
my head the earliest such system I can think of is Thoth (which
predates Idris by almost 2 years), but again I'm not sure if it was
actually the first.