Features: All common router features are supported, including traffic-shaping and QoS tools, as well as features useful on high-end networks such as VLAN tagging and polling. Boot time is fast: 30 seconds tops to a full working system on flash-based hardware. Most useful is the sophisticated Web interface, which includes the ability to upgrade the firmware directly through a browser.
M0n0wall is also the basis for a number of spin-off builds. Most notable among them is PfSense, which is intended for full-blown PC-style systems rather than embedded hardware. If you plan to repurpose a PC as a router, start with pfsense instead of M0n0wall, as you'll have something built directly for PC hardware and you can keep the amount of tinkering to a minimum. Another version, M0n0wall-mod, adds new WAN options such as the ability to configure DHCP and PPTP over a separately enumerated WAN interface.
Limitations: One drawback of M0n0wall is its support for only a small number of wireless chip sets. That said, any 802.11 hardware based on the Atheros chip set should work.
Recommendation: Those repurposing old PC hardware as a firewall or router should check out pfsense. If you're looking to fashion an embedded hardware router into a multipurpose network device, M0n0wall is a good choice.
Based on FreeBSD, M0n0wall and spin-off PfSense (setup screen shown) are designed for both embedded hardware and full-blown x86 boxes.
VyattaVyatta is a Linux-based network operating system available in both a core open source implementation and a commercial edition. The commercial edition can be had in the form of a software subscription or by purchasing a hardware appliance. Vyatta is commonly deployed as a small- or branch-office gateway, as a VPN concentrator, and as a bridge between data centers or between data centers and clouds.
Supported hardware: Like OpenWRT and M0n0wall/PfSense, Vyatta comes in incarnations that allow it to be used in stock 32-bit x86 PC hardware, so any such system can be transformed into a high-efficiency router, firewall, and network services box.