Were you thinking of Checkpoint (Nokia) IPSO[0]?
The earlier versions were based on FreeBSD 2.2.6.
Recent F5 systems are running CentOS 6.
Centos 7 starting around version 14.
Way way back they used to be on BSD. Then they moved to centos for cough cough cough (possibly NDAed) cough cough.
It's not a huge deal which because the host OS isn't anywhere in the dataplane.
Or maybe that’s Citrix.