Tails is a Linux-based operating system built around Tor.
It is designed to be used as a system live-booted from a USB drive. When the drive is unplugged, it automatically shuts down the machine. The idea is if there is a sudden situation that will compromise the information you’re working on, you can quickly un-plug the USB drive instead of fiddling with shutdown menus.
Other than an encrypted section, it keeps everything in RAM as ephemeral storage, and everything is lost on a reboot.