This is the structure of the source code:

src/ -> source code

.../zfs-fuse/ -> main zfs-fuse process

.../cmd/        -> filesystem related programs
......./zdb/    -> zdb, the zfs debugger
......./ztest/  -> ztest, the zfs tester
......./zfs/    -> zfs, filesystem management
......./zpool/  -> zpool, pool management

.../lib/                  -> libraries
......./libavl/           -> AVL trees, used by almost all ZFS libraries
......./libnvpair/        -> Name-value pairs, used by almost all ZFS libraries
......./libsolcompat/     -> Solaris headers/code not available in Linux
......./libsolkerncompat/ -> Solaris kernel headers/code necessary for the zfs-fuse process
......./libumem/          -> Memory management library
......./libuutil/         -> Solaris userland utility functions
......./libzfs/           -> ZFS library used by zfs and zpool
......./libzfscommon/     -> Common ZFS code between libzpool and libzfs. Compiles into libzfscommon-user and libzfscommon-kernel.
......./libzpool/         -> Main ZFS code. Compiles into libzpool-user (used by zdb and ztest) and libzpool-kernel (used by zfs-fuse process). Also contains "userland" zfs_context.h.