NetBSD and FreeBSD came out in 1993, the same year as Slackware. The BSDs seem like pretty complete Unix systems and are still in use today, but they are also-rans compared to GNU/Linux.
FreeBSD had to reboot the project after some lawsuits -- FreeBSD 2.0 is a different codebase from FreeBSD 1.1
It was a huge setback for every kind of adoption
I didn't actually know that the FreeBSD project had to "reboot" - this is very interesting and adds to the "lawsuit" theory.