SecBSD - Security BSD for network security testing based on CURRENT OpenBSD released monthly. It's self described as "for Ethical Hacking & Pentesting." It's only available for the AMD64 architecture.
Started in December 2018; first release in February 2019. Its first release was announced on
UnitedBSD.com. This OS is based worldwide. It's maintained by Dark Intelligence Team.
There's an episode from the podcast Hacker Talk interviewing a developer to SecBSD BSDBandit from September 2022:
https://www.jiosaavn.com/shows/secbsd-the-penetration-testing-distribution-for-the-bsd-community-|-bsdbandit-on-hacker-talk/1Gk7AV-EH-E_. He started developing for SecBSD later in 2019.
Other BSD
DamnSmallBSD is a BSD operating system, which looks like is being revived.
https://damnsmallbsd.org/ also keeps track of other BSD operating systems, including defunct ones, especially lightweight BSD's.
NetBSD based
Hardly anything is based off of it, except OpenBSD. There are a few commercial operating systems based on NetBSD.
https://www.netbsd.org/gallery/products.html
RiscOS - while this operating system for Arm64 didn't originate off as a BSD, it has imported kernel components and other parts from NetBSD. Open sourced in 2018.
OS108 - open source operating system based on NetBSD.
FDGW - is a Japanese derivative of NetBSD for floppy disks which last major activity was in 2013. It's still available.
smolBSD - a tool to create custom light VM images from NetBSD.
BlackBSD, EdgeBSD, NetBSD LiveCD, and Jibbed are defunct or no longer maintained operating systems that were based on NetBSD.
PocketSan is an operating system with major activity from 2 decades ago hosted by DamnSmallBSD.
Defunct OpenBSD based
MirOS was based on OpenBSD. Bitrig, AErieBSD, LibertyBSD, OliveBSD, Anonym.OS, isotop & ekkoBSD are other defunct operating systems that were based on OpenBSD. MicroBSD was a tool to make customized OpenBSD installs.