Best Open-Source Firewalls 2026: 6 Options Compared

People searching for an open-source firewall mean two different things, and the list below covers both. The first is a network firewall that sits at the edge and replaces a commercial appliance. OPNsense, pfSense CE and OpenWrt do that job: they route traffic, filter it between zones, and add VPN and NAT. The second is a host or application firewall on one machine, where OpenSnitch on Linux, Portmaster on Windows and Linux, and simplewall on Windows ask or control which programs may connect out. Choose by where the traffic you care about passes. If you want to protect a whole office or lab, an edge firewall on its own hardware is the answer, and OPNsense and pfSense CE need a spare PC or an appliance. OpenWrt is different: it is router firmware, so you need a supported router and the work of flashing it. If you only want to stop one laptop calling home, an application firewall is simpler and quicker to try. The common risk is misconfiguration. Open-source firewalls give you control, but a rule written in a hurry can lock you out, so keep console access and a configuration backup before you change anything on a remote box.

OPNsense

BSD-2-Clause and FreeBSD-based, a full edge firewall you run on your own hardware. It replaces an appliance rather than endpoint protection, so you need a machine with multiple network ports.

Price: Free (OPNsense pricing, checked 2026-10-22).

Platforms and license: Self-hosted firewall (FreeBSD-based). BSD-2-Clause (open source) (license source).

Project activity: 4.8k GitHub stars · last commit Oct 27, 2026

Best for: Offices and home labs replacing an appliance.

Worth knowing: Replaces a firewall appliance, not endpoint protection.

pfSense Community Edition

Apache-2.0 community edition, the other widely used FreeBSD-based edge firewall in this list. The download goes through Netgate's store, and commercial support is sold separately without published prices.

Price: Free (pfSense Community Edition pricing, checked 2026-10-22).

Platforms and license: Self-hosted firewall. Apache-2.0 (open source) (license source).

Project activity: 5.8k GitHub stars · last commit Mar 31, 2026

Best for: Admins already comfortable with pfSense.

Worth knowing: Download goes through Netgate's store; commercial support is sold separately without published prices.

OpenWrt

GPL-2.0 router firmware that handles routing and filtering through its firewall4 component, which builds nftables rules. It runs on supported routers, not on a spare PC, so check the hardware table first.

Price: Free (provided without any monetary cost; you need a supported router) (OpenWrt pricing, checked 2026-10-23).

Platforms and license: Router firmware (supported devices). GPL-2.0 (open source) (license source).

Project activity: 29k GitHub stars · latest release v25.12.6 (Oct 18, 2026) · last commit Oct 27, 2026

Best for: Replacing the firmware on a home or small office router.

Worth knowing: Firewall is firewall4 (fw4), which builds nftables rules from its config. It replaces router firmware rather than running as an app on a PC.

OpenSnitch

GPL-3.0 interactive outbound firewall for GNU/Linux, inspired by Little Snitch. It asks before each program connects, which is powerful on a desktop but noisy on a server.

Price: Free (free, open source) (OpenSnitch pricing, checked 2026-10-22).

Platforms and license: Linux. GPL-3.0 (open source) (license source).

Project activity: 14.2k GitHub stars · latest release v1.8.0 (Dec 15, 2025) · last commit Jul 26, 2026

Best for: Linux desktops that need outbound control.

Worth knowing: Interactive outbound firewall inspired by Little Snitch; GNU/Linux only.

Portmaster

GPL-3.0 application firewall for Windows and Linux with a free forever plan. Plus is 40 EUR a year and Pro is 8 EUR a month or 80 EUR a year, adding history and bandwidth visibility.

Price: Free (Free forever plan); paid from EUR 40 per year (Plus) (Portmaster pricing, checked 2026-10-22).

Platforms and license: Windows, Linux. GPL-3.0 (open source) (license source).

Project activity: 14k GitHub stars · latest release v2.2.3 (Aug 14, 2026) · last commit Oct 27, 2026

Best for: Windows or Linux users who want a polished app firewall.

Worth knowing: Pro is 8 EUR per month or 80 EUR per year; paid tiers add network history and bandwidth visibility.

simplewall

GPL-3.0 and Windows-only, a thin front end for the Windows Filtering Platform. The project describes it as for advanced users, and no paid tier is listed.

Price: Free (free, open source) (simplewall pricing, checked 2026-10-22).

Platforms and license: Windows. GPL-3.0 (open source) (license source).

Project activity: 9.2k GitHub stars · latest release v.3.8.7 (Aug 8, 2025) · last commit Oct 27, 2026

Best for: Windows users who want a small, free outbound firewall.

Worth knowing: Configures Windows Filtering Platform; described as for advanced users.

Which one to pick

• You want to protect a whole network with a dedicated box: OPNsense
• You want a router that does more than the stock firmware: OpenWrt
• You want to see what a Linux desktop connects to: OpenSnitch
• You want a friendly outbound firewall on Windows: Portmaster
• You prefer the pfSense interface and already know it: pfSense Community Edition