OpenZFS isn't some magical new code-base today but is an organization founded by FreeBSD, OS X, and Linux developers who have been working on ZFS file-system support either through FreeBSD's support, the Illumous source tree, or the ZFS On Linux project, etc. OpenZFS is the new community around all of these related open-source ZFS projects.
Also engaged with this community project is Matt Ahrens, one of the two original ZFS file-system developers at Sun that since left the company.
More details on the OpenZFS project can be found from their announcement today. Hopefully this will propel the growth of ZFS on Linux, but it's still not likely to go too far without upstream acceptance due to GPL incompatibilities and other frights from Oracle. Regardless, our latest ZFS Linux benchmarks against EXT4 and Btrfs can be found from just a few weeks ago using ZFS On Linux.