The ports tree, ZFS, jails, pf, and the internals of a Unix built for correctness.
pkg 1.0 arrived August 30, 2012 after two years and 2,000 commits; FreeBSD 10 removed pkg_install and used pkg(7) to bootstrap the new manager.
FreeBSD 5.0 shipped January 19, 2003 with SMPng's core locking architecture, while Giant remained widespread and release engineers advised caution.
How FreeBSD PF evaluates rules, creates state, uses tables and anchors, performs NAT, logs decisions, and supports safe remote changes.
How FreeBSD Ports recipes, official pkg repositories, custom options, branches, locks, audits, and poudriere fit into one package workflow.
How FreeBSD moves changes through CURRENT, STABLE, releng branches, freezes, release candidates, and supported production releases.
How FreeBSD ZFS pools, vdevs, datasets, snapshots, replication, scrubs, ARC, and boot environments behave in real operations.