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

Apple's Java implementation. Currently supports JDK1.3 and native "Aqua" look and feel on MacOS X.

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

A Java Virtual Machine (JVM) that supports Just In Time (JIT) compiling. [Open Source, MPL].

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 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]

Provides free developer kits for creating and testing Java applets and applications on a number of platforms, including AIX and Linux. Also other Java tools. [Freeware]

Information on getting Java (Kaffe) to run on Amiga computers.

A Java virtual machine implementation that converts class files into C source files using the Soot Java bytecode analysis framework, compiles them with GCC, and loads them using a built-in ELF object file loader. [Open source, LGPL]

Contains releases of the Sun JDK version 1.1.8 for the NetBSD/i386 platform. [Freeware]

Combines the jJOS kernel and decaf virtual machine. [Open Source]

Enabling the integration of pure Java into Microsoft .NET applications. Tools support J2SE or J2EE, allowing .NET code to access J2EE facilities including EJBs, and JNDI. SE (Standard Edition) and EE (Enterprise Edition) versions.

Java Virtual Machine. Works on many platforms and includes Just-In-Time (JIT) support for most of them. PersonalJava 1.1 compliant (but does not fully support the Java 2 Platform). [Open Source, GPL]

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

Java VM Just-in-Time Compiler, only for Solaris 2.5+ running on UltraSPARCs. Partially supports JDK1.1, but no AWT or Swing, and no bytecode verifier. [Open Source, BSD-like]

Provider of embedded and realtime JVMs. Provides news and evaluation kit download.

Extending the Mozilla plug-in architecture to allow Java virtual machines to be plugged into Mozilla-based browser releases. [Open Source, MPL]

Open source research infrastructure for dynamic compiling and memory management; supports programs compiled to bytecode and linked with GNU Classpath libraries. [SourceForge, Open Source, Intel]

JIT plugin for the Sun JVM, for Linux and FreeBSD on x86 processors. Includes support for a transparent distributed object system, MetaVM. [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]

Open source implementation of the Java runtime. Includes links to other open source resources.