FreeBSD Setup
FreeBSD is one of the most popular branches of the BSD project, and one of the oldest open-source branches. It emphasizes security through design and offers a featureful packaging toolchain.
Installation
Grab an image from the official repositories. You likely will want either the -memstick.img or the mini-memstick.img images. The former is larger, the latter requires an internet conection during installation.
While ARM's aarch64 (a.k.a. armv8) is not a Tier 1 supported platform, pre-built images are available for all major versions of the Raspberry Pi. Just keep in mind that it isn't possible to upgrade the release in-place.
dd the image onto your device, and the rest will explain itself.
Administration
Software Installation
Official repositories are managed with the pkg package manager. To update installed packages, use pkg update && pkg upgrade. To add a package such as HAProxy, use pkg install haproxy.
The ports project maintains a hierarchy of Makefiles to compile a much larger variety of packages on FreeBSD. To initialize the ports hierarchy locally to /usr/ports, run portsnap fetch && portsnap extract. Subsequently, to update the hierarchy, run portsnap fetch && portsnap update.
Alternatively, clone the Subversion repository of the ports project.
pkg install subversion svn checkout https://svn.FreeBSD.org/ports/head /usr/ports
Use pkg version -l "<" to list ports packages that are out of date.
Services
FreeBSD uses BSD init for services. To enable SSH, edit /etc/rc.conf with:
sshd_enable="YES"
This enables the service. To start it immediately, run service sshd start.