A solid state computer...
And this is also very cool: "[A] completely silent and super-efficient diskless computer run without any information permanency."
There's a version of Linux (a derivative of Debian, I think) that is 50megs total. DSL (Damn Small Linux).
Cooler still, they set it up to boot from a USD drive.
Coolest of all, the developers have started branching out into hardware, developing this computer that has no floppy drive, no CD-ROM drive, and no hard drive. It has an internet connection and USB ports... You put in your USB drive, boot up linux, work on your sensitive data (save it to the USB drive, of course) and can pull out the drive and walk away... Neat.