A Java 2 (JDK 1.3/1.4) compatible virtual machine. joeq is unique in that it is almost entirely implemented in Java, making it reliable and efficient. It is also language-independent, so code from any language can be seamlessly and dynamically compiled.
This interface will allow you to write code to retrieve and send promiscuous network packets from your Java program. It could provide a starting point for a java nmap or such...