slkvm is an application to provide some system tools to work with clustering and virtualization. It focuses on depending on as few external tools as possible but to also support as many virtualization technologies as possible. It works in a cluster environment where heartbeat runs virtual machines of nodes that have failed. It builds an "unheaded" cluster to avoid having a clear point of failure. It is able to build a two node cluster with everything redundant. It avoids compiling a new kernel or newer version of applications, so you can benefit from Debian security updates.
Collax V-Cube+ is a HA cluster management suite based on a 64bit Linux system and KVM to provide server virtualization. It offers solutions for single virtualization hosts, as well as high availability management on two or more nodes, allowing embedded HA storage using DRBD and iSCSI. By using live snapshots, automatic live migration, and incremental backups, the availability of virtual machines is increased tremendously in case of hardware and software maintenance or even hardware failures. Virtual network switches and the protocols GVRP, LLDP, and RSTP help to set up a virtual DMZ.