Describe: Mac OS Runtime for Java (MRJ) 2.2 is Apple's implementation of the Java Virtual Machine (JVM), based on Sun Microsystems' Java 1.1.8 specification. MRJ provides the runtime software needed to run Java applets and applications, and the Apple Applet Runn...Mac OS Runtime for Java (MRJ) 2.2 is Apple's implementation of the Java Virtual Machine (JVM), based on Sun Microsystems' Java 1.1.8 specification. MRJ provides the runtime software needed to run Java applets and applications, and the Apple Applet Runner, a simple utility for running applets without the overhead of a browser. Fast download mrj software developer kit office.