Calculate Linux Scratch (CLS) and Calculate Scratch Server (CSS) are specialized distributions designed to build a liveCD for any task.
The distribution includes the bare minimum necessary to build a desktop (CLS) or Server (CSS): driver and utilities, libraries, source code for the Linux kernel and Portage. CLS also has a preinstalled Xorg Server and graphics libraries.
Features
The LiveCD contains an exact copy of the installation image.
CLS includes utilities for configuring, building and installing the system.
Interactive system build allows you to build a customized ISO image.
Can be installed on a USB-Flash or a USB-HDD with ext4, ext3, ext2, reiserfs, btrfs, xfs, jfs, nilfs2 or fat32.
100% compatible with Gentoo.
http://www.calculate-linux.org/main/en/cls