WhoISP

Routing Software
Freesco - FREESCO (stands for FREE ciSCO) is a free replacement for commercial routers supporting up to 3 ethernet/arcnet/token_ring/arlan network cards and up to 2 modems.
KarlNet - KarlNet's product line consists of several essential networking products with state-of-the-art features that enable OEM's and resellers to create their own networking solutions for their customers.
Linux Router Project - A networking-centric micro-distribution of Linux. LRP makes building and maintaining routers, access servers, thin servers, thin clients, network appliances, and typically embedded systems next to trivial.
MikroTik Wireless & Routers - PC router software. Basic version is free. Firmware version available.
NetNimble WRIP - This is just a snapshot of my working stripped down LRP-inspired floppy disk bootable Linux 2.0.36 kernel with PCMCIA setup to run wireless radios cards.
Zebra - Free routing software distributed under GNU General Public License. An implementation of ospf and bgp for various unices. Configures like a cisco.