Tails: Portable, encrypted and secure through the Tor network
Official website tails.net
Our take
Tails is the tool when you need to leave no trace on the machine you are using: boot it from a USB stick, route everything through Tor, and the session vanishes on shutdown. The amnesia is the whole point and also the catch, since nothing persists unless you set up encrypted storage on purpose, and like all Tor it is slow. Use it for a clean, throwaway anonymous session on hardware you do not own; do not expect it to be your everyday OS.
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Tails alternatives
Qubes OS Qubes OS: A reasonably secure operating system
Whonix A free, open-source desktop operating system that forces all traffic through Tor, run as two isolated virtual machines.
Fedora Workstation Fedora Workstation: User friendly and easy to setup
Ubuntu Ubuntu: User friendly and easy to setup
openSUSE Tumbleweed openSUSE Tumbleweed is a rolling-release Linux distribution that defaults to Btrfs with Snapper snapshots, letting you boot into a previous system state if an update breaks something. Available with KDE, GNOME, or Xfce.
Arch Linux Arch Linux is a minimal, rolling-release Linux distribution built around a do-it-yourself philosophy. You assemble the system yourself from a bare base, choosing every component, and keep it current with the pacman package manager.