pfSense

pfSense (stewarded by Netgate) is an absolute, unquestioned legend, a massive cult phenomenon, and the undisputed titan of the "Open-Source Firewall" market. While Palo Alto and Cisco charge tens of thousands of dollars for proprietary hardware and software licenses, pfSense is a completely free, open-source firewall distribution based on FreeBSD that anyone can download and install on an old Dell computer. The absolute core differentiator of pfSense is "Limitless Power without Licensing Fees." There are no artificial software limitations. If you want to configure 500 complex IPsec VPN tunnels, load-balance 4 different internet connections (Multi-WAN), and run deep Suricata Intrusion Prevention (IPS), pfSense allows you to do it entirely for free. The only limitation is the physical CPU power of the hardware you install it on. Because it is completely free of recurring subscription traps, it is heavily utilized by massive university labs, bootstrapped tech startups, highly advanced home-lab enthusiasts, and cost-conscious regional ISPs. For organizations that have highly skilled networking engineers on staff but refuse to pay exorbitant enterprise "per-user" or "throughput" licensing fees, pfSense is a staggering, industrial-grade powerhouse.