Revelo – Javascript Deobfuscator
While this tool does have some protections built into it, it may execute malicious code that could harm your computer so use it in a virtual machine. It’s been tested to run on Windows XP. There’s a helper document inside the zip file which includes safe samples to play with.

* Analyze a script quickly by loading a file or pasting in Javascript code
* Includes several methods to deobfuscate Javascript
* Includes a built-in browser proxy which displays the URL of outgoing requests
* Displays the Document Object Model (DOM) elements
* Includes a packet sniffer which logs incoming and outgoing requests
* Includes a software firewall to prevent the program from accessing Internet content accidentally
* Ability to act as a web proxy to catch and block redirects
* Beautifies Javascript code to make it more readable
* Ability to clear the browser cookies
* Ability to spoof the user-agent string