OPNSense is an open source operating system that can be used to build a firewall appliance. When installed on a dedicated computer (typically with at least two network cards), it can provide protection and monitoring for an entire network. OPNSense includes "captive portal" features that can be used to manage a public wifi network. It also incorporates network traffic monitoring using the industry-standard Netflow system. OPNSense administrators can also enable category-based web filtering (e.g. for school networks). A number of VPN options are included as well, including OpenVPN, IPsec, L2TP, and PPTP. All of OPNSense's features are configured through a web-based interface for which extensive online documentation is available. The smallest machine that can run OPNsense will have a 500MNz intel processor with 512MB of memory and 4 GB of storage. For full functionality, the OPNSense project recommends a 1.5 GHz intel processor, 4GB of memory, and 120GB of storage.