See also: Encrypting Your Network Links
Acronym: Crypto IP Encapsulation
CIPE is an ongoing project to build encrypting IP routers. The protocol used is as lightweight as possible. The protocol creates encrypted IP over UDP tunnels and is not as flexible as IPSEC, however CIPE is easier to setup and works over NAT and SOCKS. The project is currently active, with a win32 version in development.