Tails OS

The Amnesic Incognito Live System — a privacy-focused OS that boots from USB and forgets everything when you shut down. Tails is amnesic and session-based, suited to a public or shared machine; for a persistent setup on a dedicated machine you control long-term, see Whonix.

Features

Runs entirely from USB
Leaves no trace on computer
All traffic routed through Tor
Built-in encryption tools

The "leaves no trace" claim is mechanical, not marketing: Tails runs entirely from RAM and wipes RAM on shutdown. Nothing from your session is written to the host computer's hard drive unless you explicitly enable persistent storage (see below).

Installation

Download Tails from tails.boum.org
Verify the download — a tampered ISO is a realistic attack vector; skipping verification defeats much of the point of using an amnesic OS. Tails provides two official methods: the Tails Verification browser extension, or checking the ISO against the official OpenPGP signature published by the Tails project. Step-by-step instructions are on tails.boum.org alongside the download.
Create bootable USB
Boot from USB
Configure persistent storage (optional) — see "Persistent Storage: What It Actually Trades Off" below

Persistent Storage: What It Actually Trades Off

Without persistent storage, Tails forgets everything on shutdown — true amnesia. Enabling it creates an encrypted partition on the USB that survives reboots, so you can keep PGP keys, bookmarks, or persistent app settings between sessions.

That convenience has a cost: anything stored there is now something a seized device could contain — encrypted, but present. It is a real tradeoff against pure amnesia, not a free upgrade. Enable only the persistent features you genuinely need (for example, a GnuPG key or a small set of bookmarks), and leave the rest off.