ZFS was originally created at Sun and open sourced.  Sun was absorbed by Oracle and stopped being open (or even really existing), so ZFS was taken up by several separate groups – FreeBSD and Illumos being two examples.  OpenZFS has been announced, in part to provide common reference for other platforms that might implement it and probably to avoid capability fragmentation.  It’s certainly a good idea.

(If I have my history wrong, please correct me.)