A free live distro
RMS GNU/Linux is aiming to be the best libre live distro out there. it's based on Slax(the name is an acronym, RMS's Mostly Slax.)It's built on a modular concept where just about anything could be replaced quite easily, it currently boots from either flash drive or CD, though we've had a report of a successful hard drive install too.
How to get started
You can try making modules, getting source code, making art, you can really do whatever. Hanging out on #rmsgnulinux@freenode is a good idea for finding out what's needed at that moment.