It’s basically a linux kernel but a bsd userland & filesystem layout. That’s not strictly true in practice but close enough. Their other guiding ethos was to minimise package maintainer patches so you’d get more vanilla software than in other distros.
Having said that, i run FreeBSD 13 for a nas / firewall at home (only really so i don’t lose the muscle memory) but the bsd init system feels distinctly utilitarian to me in comparison to systemd / launchd (macos) or even smf (solaris - RIP).
As a developer systemd is very attractive, you get so much useful functionality for free, socket management, privs, capability management - stuff that you usually want to use but would rather outsource than write yourself.
[1] https://wiki.archlinux.org/index.php?title=Initscripts/rc.co...