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ILSpy is the open-source .NET assembly browser and decompiler.

What's Cool about dotPeek?Decompiling .NET 1.0-4.0 assemblies to C#Quick jump to a specific type, assembly, symbol, or type memberEffortless navigation to symbol declarations, implementations, derived and base symbols, and moreAccurate search for symbol usageswith advanced presentation of search resultsOverview of inheritance chainsSupport for downloading code from source serversSyntax highlightingComplete keyboard supportdotPeek is free!

JustDecompile is a stand-alone, free decompiling tool which converts assemblies into source code.

The “Java Decompiler project” aims to develop tools in order to decompile and analyze Java 5 “byte code” and the later versions.

.NET Reflector is a class browser and analysis tool for .NET. It allows developers to navigate, search, disassemble and analyze .NET components.

This is a tool to open Java class file binaries, view their internal structure, modify portions of it if required and save the class file back. It also generates readable reports similar to the javap utility. Easy to use Java Swing GUI. The user interface tries to display as much detail as possible and tries to present a structure as close as the actual Java class file structure. At the same time ease of use and class file consistency while doing modifications is also stressed. For example, when a method is deleted, the associated constant pool entry will also be deleted if it is no longer referenced. In built verifier checks changes before saving the file. This tool has been used by people learning Java class file internals. This tool has also been used to do quick modifications in class files when the source code is not available. »

Free Zend Guard decoder, Free Java class decompiler, Free Adobe Flash swf decompiler, Free .NET (Dot NET) decompiler

A suite of Java metaprogramming tools focused on code generation, analysis, and decompilation.

The MSIL Disassembler is a companion tool to the MSIL Assembler (Ilasm.exe). Ildasm.exe takes a portable executable (PE) file that contains Microsoft intermediate language (MSIL) code and creates a text file suitable as input to Ilasm.exe.