Routing

CIPE
An ongoing project to build encrypting IP routers. Software is already available for Linux and released under GPL.
http://sites.inka.de/sites/bigred/devel/cipe.html

GNU Zebra
Manages TCP/IP based routing protocols. It supports BGP4 (RFC1771), RIPv1, RIPv2 and OSPFv2. Zebra makes use of OS threads where available.
http://www.zebra.org/

Unofficial GNU Zebra FAQ
GNU Zebra documentation, not included into releases, but useful and up-to-date. General dynamic routing information included.
http://pilot.org.ua/zebra