There are several popular alternatives to OPNsense in the firewall and network security space. Here are some of the most notable ones: pfSense: Very similar to OPNsense (OPNsense is actually a fork of pfSense) Untangle Sophos XG Firewall IPFire Shorewall Endian Firewall VyOS Cisco ASA Fortinet FortiGate Palo Alto Networks Firewalls