Slax is small Live Debian-based Linux distro that can be regarded as the Minimalist’s OS. It is Live because you can run it right from a USB stick and it works with a plethora of filesystems including NTFS, FAT, EXT (ext2,ext3,ext4), and btrfs.
It was developed by Tomas Matejicek from the Czech Republic with a Monolithic kernel type to be fully customizable using Slackware packages and Slax modules – which, of course, are also open-source.