I hate to be that guy, but Slackware has been around for longer than FreeBSD, it beats it by a few months. One of Slackware's goals is to be Unix-like, and that decision is definitely evident in the distribution.
Thanks for pointing that out! Post updated. Slackware was first distro I ever used seriously, after getting hooked up on Linux with a Red Hat 5.0 or 5.1 CD that was attached to a (printed) IT monthly newspaper. I have to tell, FreeBSD feels kind of similar to Slackware.