What other open source research VMs for the Java platform are there?
All the VMs mentioned in the preceding paragraph are open source. Furthermore, there are many research and experimental VMs that are not written in Java. Please forgive us if we do not list them all! Here are just some examples: • The Apache Harmony project contains a VM written in C++. • Kaffe and its many variants. • ORP • CACAO And last but not at all least, the HotSpot VM from Sun is now also open source as part of OpenJDK.