For something approaching 20 years, I’ve used OpenBSD to firewall my network from the internet and provide basic network services (DHCP, DNS, NTP, VPN, etc.). Just recently I’ve decided to retire OpenBSD and stand alone computers from the role of firewalls for something smaller, lower power, and easier to manage and upgrade.
I’ve been steadily moving towards smaller and lower power systems for as long as I’ve been doing OpenBSD based firewalls. My first machines were nothing more than mid-tower desktops that I had upgraded away from. In 2000-2003 I made my first moves towards building something more specialized, when I switched from using old towers to building a specific micro-atx pizza box style machines; though still with standard Athlon XP CPUs and parts.