Tails is a live operating system that aims to preserve your privacy and anonymity. It helps you to use the Internet anonymously and circumvent censorship almost anywhere you go and on any pc but leaving no trace unless you ask it to explicitly.
It is a complete OS designed to be used from a DVD, USB stick, or SD card independently of the computer's original operating system. It is Free Software and based on Debian GNU/Linux.
Tails comes with several built-in apps pre-configured with security in mind: web browser, instant messaging, email client, office suite, image and sound editor, etc.