Implementations Standard Edition
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Apple Java support - Apple's Java implementation. Currently supports Java 5 and native "Aqua" look and feel on MacOS X.
FreeBSD Java Project - The official port of Sun's JDK to FreeBSD.
HP-UX Java Ports from HP - Version 1.3 available.
Java 2 Platform - Sun Community Source Licensing - Sun's source code for their implementations of the Java 2 Platform, Standard Edition, available free of charge.
Java Technologies on SCO Systems - JDKs for SCO systems.
Java Technology Software from HP - For Tru64 Unix, OpenVMS Alpha, Windows NT/Alpha and Linux/Alpha.
Java(TM) 2 Platform, Standard Edition (Win32/Solaris/Linux) - Sun's official page for the Java 2 Platform, Standard Edition (also known as JDK 1.2), with free downloads for Windows 95/98/NT/2000, Solaris and Linux.
JRockit - Highly scalable virtual machine with dynamic code optimization, available for WinNT/2000 and Linux. [Commercial]
MacOS Runtime for Java (MRJ) - Apple's official MRJ.
Natural Bridge - A system for statically compiling and linking JVM bytecode applications. It includes an optimizing ahead-of-time compiler, a linker and recompilation manager, an advanced thread-hot runtime, and a core set of optimized libraries compatible with SunTM's Java 2 release. (Win32 only). [Commercial]
Novell JVM for NetWare. - Offers Novell supported runtimes for NetWare. Help build the largest human-edited directory on the web.