Jad stands for “Java decompiler”. Java decompiler is a program that reads one or more Java class files and converts them into Java source files. Jad is a 100% pure C++ program and it generally works several times faster than decompilers written in Java. Jad doesn’t use the Java runtime for its functioning, therefore no special setup is required (like changes to the CLASSPATH variable). Jad is a standalone command-line utility, but can be integrated in some IDEs (see below).
Jad was originally developed by Pavel Kouznetsov in 1997. The latest version (1.5.8) was released in 2001, and the last maintenance release (1.5.8g) was out in 2006. The official Jad homepage (URL: http://www.kpdus.com/jad.html) is unavailable since February 2009.
However, the latest page snapshot (January 2008) can be found in the web archive. (Update – Feb 2012: For some reason Web Archive obeys “robots.txt” placed on kpdus.com by the current owner, so the old site snapshot was made unaccessible…) Also, Tomas Varaneckas provides alternative download location for recent Jad versions on his site.
Eclipse integration is provided by JadClipse plug-in. Last stable version (currently – 3.3) can be downloaded from the project’s download page. Main project page says that preview of version 3.4 was released in February 2009, but I was unable to find downloadable version (except the project sources).