It is really confusing and it seems like they all share the same illumos as their common upstream. [0]
I wonder what kind of 'scope' illumos has in comparison to the BSDs. The BSD's base installations seem to be complete OSes with some additional bits from 3rd parties but the table at [0] shows that these illumos distros differentiate between the used package manager and even the default userland.
Is there a reason why these Solaris forks tend to use the GNU userland instead of pushing their own like the BSDs?