illumos is the repo of record for OpenZFS[1], which is the community fork of OpenSolaris' ZFS (which is now proprietary). Most of the really cool new features are in OpenZFS because it has far more developer involvement (from FreeBSD, illumos, etc).

[1]: http://open-zfs.org/wiki/Main_Page

No: http://open-zfs.org/wiki/Main_Page

Illumos is a fork of OpenSolaris: https://wiki.illumos.org/display/illumos/illumos+Home

Basically ZFS is Solaris (Oracle), everything else is OpenZFS. And every Solaris-like OS is at best just going to be an OpenSolaris (or derivative) fork.

No, they split when Oracle bought Sun. The only part of OpenZFS, which everything but Solaris uses, that involves Oracle is a number of patents that the CDDL grants permission to use.