XORP is described as '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 the only open source platform to offer integrated multicast capability' and is an app in the network & admin category. There are four alternatives to XORP for Linux, BSD, Mac and Windows. The best XORP alternative is Quagga, which is both free and Open Source. Other great apps like XORP are BIRD, FreeRouter and ExaBGP.
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.
Quagga is the most popular Linux alternative to XORP.
Quagga is the most popular Open Source & free alternative to XORP.
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 an open source routing suite supporting ospf, isis, rip, bgp, mpls, te, segment routing and a lot more.
FreeRouter is the most popular Windows alternative to XORP.
exabgp - The BGP swiss army knife of networking.
Unlike BIRD or Quagga, ExaBGP was not designed to transform a general purpose server into a router, but to allow engineers to control their network easily. Think of it as Software Defined Networking for people with usual BGP route.
ExaBGP is the most popular Mac alternative to XORP.