FreeRouter!

Quagga is a network routing software suite providing implementations of Open Shortest Path First (OSPF), Routing Information Protocol (RIP), Border Gateway Protocol (BGP) and IS-IS for Unix-like platforms, particularly Linux, Solaris, FreeBSD and NetBSD.

BIRD is an open source implementation of a TCP/IP routing daemon for Unix like systems. It supports both IPv4 and IPv6, multiple routing tables, and a BGP, RIP and OSPF routing protocols, as well as statically defined routes.

exabgp - The BGP swiss army knife of networking.

XORP is an Internet Protocol routing software suite. It provides a fully featured platform that implements IPv4 and IPv6 routing protocols and a unified platform to configure them. It is the only open source platform to offer integrated multicast capability. XORP's modular architecture allows rapid introduction of new protocols, features and functionality, including support for custom hardware and software forwarding.