Hazelcast is released under Apache License and the project is hosted at http://code.google.com/p/hazelcast. It can be freely used in commercial or non-commercial applications.
Hazelcast is pure Java. JVMs that are running Hazelcast will dynamically cluster. Although by default Hazelcast will use multicast for discovery, it can also be configured to only use TCP/IP for enviroments where multicast is not available or preferred. Communication among cluster members is always TCP/IP with Java NIO beauty. Default configuration comes with 1 backup so if one node fails, no data will be lost. It is as simple as using java.util.{Queue, Set, List, Map}. Just add the hazelcast.jar into your classpath and start coding.
This lection will help you understand Hazelcat more thorougly and give you some ideas on how to utilize it to improve your clustered environment.