user-space replacement to VRRP -- automatic IP fail-over

 UCARP allows a pair of hosts to share common virtual IP addresses in
 order to provide automatic fail-over. It is a portable user-land
 implementation of the secure and patent-free Common Address Redundancy
 Protocol (CARP, OpenBSD's alternative to the VRRP).
 .
 Strong points of the CARP protocol are: very low overhead,
 cryptographically signed messages, interoperability between different
 operating systems and no need for any dedicated extra network link
 between redundant hosts.