The first set of patches are available to compile the ZFS file system module on FreeBSD. "This is a first set of patches, which allows to use ZFS file system from OpenSolaris on FreeBSD. To apply the patch you need to have recent FreeBSD source (be sure you have rev. 1.284 of src/sys/kern/kern_synch.c). To try it out you need i386 machine (this is what I tested) and kernel without WITNESS compiled in (there are probably some warnings still). Currently it can only be compiled as a kernel module."