Unix based OS

Name four Unix based OS. And if you have started thinking about Red Hat, fedora, ubuntu than... you are wrong.
Strangly. contarary to popular belief, Linux is not unix based. Any OS based on linux may be Unix like, but not Unix based.

I bet, with no money on hold, that many few could name 4 Unix based OS. Here they are:

Solaris (sun, now oracle)
Mac OS (apple)

And you have won the battle.