Free Routing Software (for BGP, OSPF and RIP, for example)

Quagga is a routing software suite, providing implementations of
OSPFv2, OSPFv3, RIP v1 and v2, RIPv3 and BGPv4 for Unix platforms,
particularly FreeBSD and Linux and also NetBSD, to mention a few.
Quagga is a fork of GNU Zebra which was developed by Kunihiro Ishiguro.
The Quagga tree aims to build a more involved community around Quagga
than the current centralised model of GNU Zebra.