PfSense is a free and open-source firewall and routing platform based on FreeBSD. It can be installed via live CD, USB, or serial connection. PfSense offers robust, highly available, free, scalable, and flexible network security management through features like firewall, NAT, VPN, DHCP server, load balancing, and multi-WAN support. It allows users to replace their existing router or firewall with an alternative that provides more control and customization of their network security and traffic routing.