JAVA BYTECODE DECOMPILERS

Decompilers that read Java bytecode programs usually decompile to Java, since that is the language that the majority of such programs are written in. However, the source language could have been any of a large number of languages; see [other languages for the Java VM.
Jdec is a Java decompiler. It can be used to decompile the bytecodes present in a .class file to produce a Java source file which can be nearly correct or equivalent (due To different interpretations) to the original Java source. It also has a good UI. It is hosted on SourceForge. Currently Jdec is licenced under GPL. Visit the home site for any updates and current status.
JODE is an open source Java decompiler and obfuscator. Hosted on SourceForge under the GPL license. The core decompiler is under the LGPL, meaning that you can use it in a commercial decompiler. Written in Java. For tests see DecompilationJodeTest.
Jad (Jad - the fast JAva Decompiler) is a decompiler that is free for non commercial use. Source code is not provided. Its decompilation engine is used in numerous graphical front ends, including FrontEnd Plus, Decafe Pro, DJ Java Decompiler, and Cavaj. For tests see DecompilationJadTest.
Dava is a research decompiler that recovers types well and has been tested against non-Java bytecode programs.
The Mocha decompiler for Java .class files. You can use crema to scramble symbolic information in the .class files.
SourceTec Java Decompiler (formerly the Jasmine Java Decompiler) is a patch to Mocha, a well known decompiler. It is now very old; it only works on Java 1.1 classfiles. For tests see DecompilationStTest.
JReversePro is an open source Java decompiler written in Java.
SourceAgain is one of the better known commercial Java decompilers.
ClassCracker 3 is another commercial Java decompiler.
Decaf was a decompiler for Java .class files written in Ada95. Decompilers to Ada95 and Smalltalked were planned. The page was at http://ourworld.compuserve.com/homepages/teleobjet/decaf.htm. You may be able to access an archived copy at archive.org.
DCompiler (also known as JADO) is yet another Sourceforge open source decompiler; this one is in very alpha status. It will not decompile even the simplest test programs, so no tests have been performed.
WingSoft have a decompiler called WingDis and an obfuscator called WingGuard (see their products page).
The JReveal decompiler (www.jreveal.org) seems to be the Jasmine decompiler (version 1.1 of Mocha), with a web based GUI front end. I could not get the decompiler to work for me (Jan 2003), but you may have better luck. There is a small online paper and some examples; it looks like a really handy tool.