Please note that Gubcast is a Java-based tool for Web application developers. In order to make use of it, you will need some sort of Java software development environment. One possibility is Sun's own Java 2 development system, which is available at no charge here. If you only want to run the included demo system, and don't plan to develop your own Gubcast-enabled applications, then you only need a Java run-time environment such as the one provided at no charge by Sun here.