The Tails Project just released the final version of live OS Tails 2.5, a live OS system which runs on every computer and leaves no traces either on the machine or on the internet.
This particular Tails was used by a former NSA employee Edward Snowden to remain hidden on the internet.
The new version incorporates some important new features and changes, including upgrading to the latest Tor Browser 6.0.3, improvements to icedove an email suite and news.
The new version also contains many other small but useful enhancements, such as firewall and kernel hardening, and support in languages other than English. You can see the changelog of the new version from here.
Download the new operating system
https://tails.boum.org/install/os/index.en.html