pfSense is a free, open source customized distribution of FreeBSD tailored for use as a firewall and router. In addition to being a powerful, flexible firewalling and routing platform, it includes a long list of related features and a package system allowing further expandability without adding bloat and potential security vulnerabilities to the base distribution. pfSense is a popular project with more than 1 million downloads since its inception, and proven in countless installations ranging from small home networks protecting a single PC to large corporations, universities and other organizations protecting thousands of network devices.

This project started in 2004 as a fork of the m0n0wall project, but focused towards full PC installations rather than embedded hardware.