Article by David K. Friedman and David A. Wheeler. It briefly introduces Java, provides a bit of Java history, and describes various Java implementations.

Provider of embedded and realtime JVMs. Provides news and articles.

A free replacement for Sun's proprietary core Java class libraries. [Open Source, GPL with exception]

A free replacement for the "javax.*" classes (core and otherwise); sibling project to GNU Classpath. [Open Source, GPL/LGPL]

Sun Microsystems backed industry body, Java Community Process (JCP) oversees development of platform and language, voted to alter community structure, officially supporting OSS implementations of Java, JCP 2.5. [The Register]

Port of Kaffe to the BeOS platform. [Open Source, GPL]

The GNU Compiler for Java - compiles Java source or bytecode to native machine code. Most APIs are supported, except the AWT and Swing. [Open Source, GPL]

A former IBM research virtual machine focussing on compatibility, high performance, dependency analysis, and constructive assistance. Project information, FAQ, and links. [Open Source, CPL]

Java VM for Unix, more so Linux. Native threads and JIT compiling. Uses GNU Classpath. [Open Source, GPL]

Java virtual machine (VM) that runs in Linux kernel, Linux kernel module JVM, based on JOS and kissme projects. [Open Source, GPL]