The Transis group communications system - providing efficient group multicast for high-availability applications.
SCTP Stream Control Transmission Protocol (RFC 2960). From Joe Grimm: The HA features of SCTP revolve around using multi-homed hosts to provide failover paths implemented at the transport layer, essentially this becomes a transparent issue to SCTP applications. This is just one of the features in SCTP but one network standard being driving by the Carrier Grade community to provide 5 nines networking on top of the Internet. The linux kernel project to implement this can be found at: http://www.sf.net/projects/lksctp.
The IETF's Reliable Server Pools working group. The purpose of the working group is to develop an architecture and protocols for the management and operation of server pools supporting highly reliable applications, and for client access mechanisms to a server pool
Werner Almesberger's TCP Connection Passing project. tcpcp is a mechanism that allows cooperating applications to pass ownership of TCP connection endpoints from one Linux host to another one. Such functionality should be useful in load-balancing and failover applications. tcpcp can be used between hosts using different architectures and does not need the other endpoint of the connection to cooperate (or even to know what's going on).
Extended Transmission Control Protocol (ETCP). ETCP helps within migration clusters because by using it, it becomes possible to have a network connection follow a process, instead of tcp IO being relayed through the original node. Given application state synchronization, this technique could also useful for failover clusters as well.
UCARP - Common Address Redundancy Protocol (CARP) for Unix. UCARP allows a couple of hosts to share common virtual IP addresses in order to provide automatic failover.
VRRP (Virtual Router Redundancy Protocol) is a redundancy protocol designed to increase the availability of the default gateway.