In FreeBSD the base system stuff goes into /bin /lib and /etc, and all the ports target /usr/local as the prefix. Even the config files of the ports go to /usr/local/etc.
Though NixOS and Guix form a different approach than the FreeBSD's, that is they treat packages as isolated immutable objects and use an unconventional directory layout (wanted to note this, because someone who doesn't know the OSs named may have thought that FreeBSD and NixOS/Guix approaches are similar).
