JavaRa is a simple tool that does a simple job: it removes old and redundant versions of the Java Runtime Environment (JRE).
Java software in general and the Java JRE in particular allow you to run applications called 'applets' that are written in the Java programming language. You probably have Java JRE installed on your computer because these applets allow you to play online games, chat with people around the world, calculate your mortgage interest, view images in 3D, as well as many others.
As with all software, the JRE is updated on a regular basis. Updates are necessary to add new functionalities, to remove programming bugs or to repair possible vulnerabilities.
Usually older versions of programs are removed during the install of new versions but Sun (the owner of Java) has somehow decided not to do this. The result is that a number of different versions of the JRE may exist on your computer. These older versions potentially pose a threat to your sense of security due to the possible vulnerabilities or security holes that may exist in them.
Java advises users to always have the latest version of the Java Runtime Environment (JRE). The latest version is always the recommended version because it contains updates and improvements to previous versions of the JRE. The latest available version is always compatible with the older versions.
But they also tell you that you can keep older versions of the JRE installed, in case you have an applet or an application that still depends upon a previous version. But this warning is quite useless as all applets and applications should be kept updated to ensure a maximum level of safety and security.