Later: Be the best possible packet filtering system
Evolutionary steps:
filter on all TCP/IP protocols (3.1)
authpf (per-user rules, ssh authentication) (3.1)
ALTQ (traffic shaping) integrated (3.3)
anchors (named sub-rulesets) (3.3)
tables (fast IP address lookup for rulesets) in filtering (3.3)
spamd (3.3: blacklist-only, 3.5: greylist, 3.7: greytrapping, 4.1: sync)
packet tagging (3.4)