MultiBoot USB
This is a collection of GRUB scripts that allows to create a bootable pendrive (USB dongle, flash stick) supporting a number of different OS images. Simply copy ISO files under `/iso-imgs`. Both UEFI and Legacy BIOS boot modes can be enabled simultaneously.
Porteus is a fast, portable and modular live CD/USB medium based on Slackware Linux. The distribution started as a community remix of Slax, another Slackware-based live CD, with KDE 3 as the default desktop for the i486 edition and a stripped-down KDE 4 as the desktop environment for the x86_64 flavour. The lightweight LXDE is available as an alternative desktop environment.