OpenWrt is an operating system (in particular, an embedded operating system) based on the Linux kernel, primarily used on embedded devices to route network traffic. The main components are the Linux kernel, util-linux, uClibc and BusyBox. All components have been optimized for size, to be small enough for fitting into the limited storage and memory available in home routers.
pfSense is an open source firewall/router computer software distribution based on FreeBSD. It is installed on a computer to make a dedicated firewall/router for a network and is noted for its reliability and offering features often only found in expensive commercial firewalls. pfSense is commonly deployed as a perimeter firewall, router, wireless access point, DHCP server, DNS server, and as a VPN endpoint.
LibreWRT is a GNU/Linux-libre distribution for computers with minimal resources, such as the Ben Nanonote, ath9k based wifi routers, and other hardware that respects your freedom with emphasis on free software. It is used by the Free Software Foundation on their access point and router which provides network connectivity to portable computers in their office.