Knoppix is a Linux distribution that can be run from a cd-rom without having to be installed to a hard drive.

It can be installed to a hard drive if desired.

It is based off the Debian distribution.

It seems to be becoming quite popular.

The best English site for information about Knoppix seems to be http://www.knoppix.net

The official site for Knoppix is Klaus Knopper's website: http://www.knoppix.org