The Tor Browser Bundle is an easy-to-use portable package of Tor, Vidalia, Torbutton, and a Firefox fork preconfigured to work together out of the box. It contains a modified copy of Firefox that aims to resolve the privacy and security issues in mainline version.
Tor was originally designed, implemented, and deployed as a third-generation onion-routing project of the U.S. Naval Research Laboratory. It was originally developed with the U.S. Navy in mind, for the primary purpose of protecting government communications. Today, it is used every day for a wide variety of purposes by normal people, the military, journalists, law-enforcement officers, activists, and many others.