XORP!

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.

freeRouter is a routerOS process.it means freeRouter speaks routing protocols, and reencapsulates packets on interfaces.(a huge list of encapsulation and routing test cases can be found under self-test results) since it is an unprivilegized process, it receives and sends packets through sockets.there are external, privileged processes that place traffic to these sockets.(it means that internet can be used as backplane for router processes)the command line tries to mimic the industry standards with one exception: no global routing table: every routed interface must be in a virtual routing table.(positive side effect: there are no vrf-awareness questions)complex self-tests: connectivity tests executed on a network of virtual routers and these test results are compared to predefined values. »

exabgp - The BGP swiss army knife of networking.