Alternative to Clusters
Dave pointed out that Stratus has focused on a different approach, continuous processing. Continuous processing is using redundant hardware or software components to create a never-fail environment on a very simple configuration. No clustering manager is required. Potential failures are detected long before than can have an impact and are prevented. Virtual servers would simply begin execution on the other system if the original host failed.
Dave also pointed out that Stratus' ftServer family of fault tolerant computing systems are often utilized to make virtual server-based environments more highly available as well.