The security router (Halon SR) is a firewall/router software distribution based on OpenBSD. It's noted for being designed with IPv6 in mind, its rich set of features (BGP, MPLS, VRFs) often only found in more expensive products, openness (APIs and root access), and ambitious management (atomic commit/rollback).
It runs on anything
It runs on effectively any x86 computers/servers and virtualization hosts, and makes a great choice both for affordable Mini-ITX appliances (with Atom or Geode CPUs such as PC Engines' ALIX) as well as high-end servers (preferably with AES-NI for high VPN throughput). Any fast, well-designed uni-processor server with high-quality NICs (such as Intel PRO/1000) will provide several gigabits of plain-text throughput.
The security router software distribution is based on OpenBSD, and the great majority of the system is open source. After downloading, the source code may be browsed, viewed and altered by logging in using the root access. For example, patches to the kernel are made available, and the web, LCD and other interfaces are programmed in open scripting languages. Thus, everything that is externally exposed (its attack surface) is source code reviewable, which some would argue is a security advantage in itself.
The software is available as a free download. There are several pre-packaged versions that, while all containing the same system software, comes prepared for/with serial console, 64-bit CPUs, vSphere OVF container, etc. Running the software on your own hardware is as simple as writing the raw software image directly onto a memory such as a USB stick. There are both free and paid models, which include commercial support.