ZoL, if my ancient memory serves, was at LLNL, not based on the FreeBSD port (if you go _very_ far back in the commit history you can see Brian rebasing against OpenSolaris revisions), but like 2 or 3 different orgs originally announced Linux ports at the same time and then all pooled together, since originally only one of the three was going to have a POSIX layer (the other two didn't need a working POSIX filesystem layer). (I'm not actually sure how much came of this collaboration, I just remember being very amused when within the span of a week or two, three different orgs announced ports, looked at each other, and went "...wait.")
Then for a while people developed on either the FreeBSD port, the illumos fork called OpenZFS, or the Linux port, but because (among other reasons) a bunch of development kept happening on the Linux port, it became the defacto upstream and got renamed "OpenZFS", and then FreeBSD more or less got a fresh port from the OpenZFS codebase that is now what it's based on.
The macOS port got a fresh sync against that codebase recently and is slowly trying to merge in, and then from there, ???
I believe it was called ZFS On Linux or something like that.
Nice how things have evolved: from FreeBSD to linux and back. In my mind this has always been a very inspiring example of a public institution working for the public good.