SUN: Solaris Cluster (SUN Cluster) is now Opensource

SUN released the source code of the Sun Cluster on www.opensolaris.org under the name High Availability Clusters.
The project page can be found here.

If you are really interested try the wiki or the related blog.
The Open HA Cluster source code is available under the Common Development and Distribution License (CDDL). For more information follow this link to wikipedia.

Here some statements from sun about Solaris Cluster:

Previously known as Sun Cluster, the Solaris Cluster framework extends high availability features of Solaris - it includes Solaris Cluster, Solaris Cluster Geographic Edition, developer tools and support for commercial and open-source applications through Solaris Cluster agents. The integrated software provides high availability and disaster recovery for local, campus, metropolitan and worldwide clusters.

By tightly coupling Sun's servers, storage and networking solutions, Solaris Cluster provides the maximum level of service availability and performance for a cluster system.
The servers (nodes) in a cluster communicate through private interconnects. These interconnects carry important cluster information (data as well as a cluster "heartbeat"). This heartbeat lets the servers in the cluster monitor the health of the other servers within the cluster, ensuring that each server is "alive". If one of the servers goes offline and its heartbeat disappears, the rest of the devices in the cluster isolate the server and "fail-over" any application or data from the failing node to another node. This fail-over process is quick and transparent to users of the application. By exploiting the redundancy in the cluster, Solaris Cluster ensures the highest levels of availability.

Solaris Cluster Geographic Edition software enables a multi-site disaster recovery solution that manages the availability of application services and data across geographically dispersed Solaris Clusters. In the event that a primary cluster goes down, Solaris Cluster Geographic Edition enables sysadmins to start up automatically business applications with replicated data on the secondary Solaris Cluster.

I think Solaris Cluster is an alternative solution to Oracle Clusterware to achieve high availability for your software stack. But keep in mind, that the configuration of these cluster software stacks has to be planned and maintained carefully...