Tin Hat is a Linux distribution derived from hardened Gentoo. It aims to provide a very secure, stable, and fast desktop environment that lives purely in RAM. Tin Hat boots from CD, or optionally USB pen drive, but it is not a LiveCD in that it does not mount any file system from the boot device. Rather, Tin Hat employs a massive squashfs image which expands into tmpfs upon booting. This makes for long boot times, but remarkable speeds during human-computer interaction.
Portable Linux is a tool that lets you create bootable USB and removable drives using popular Live CDs based on Casper (like the Ubuntu family of distributions). It sports some unique features. The live setups it creates let you use the remaining disk space on your USB drive to store and transport files between computers, as usual. If your distribution supports persistence, the files and settings you edit on your live Linux distribution are persisted across reboots. Finally, you can access the area used to store your files from within your Linux distribution.