This is an old stuff but I decided to write this as this is one of indispensable utility for me for a long time.
It allows you to have multiple OS installer in an USB flashdisk. Although you can have several Android and Linux installer in one flashdisk, it only allowed 1 version of Windows.
The official site:
Watch out with the language, since this app is originally French, but overall is very good.
For easier method of install (Ubuntu derived / PPA) you can use:
$ sudo apt-add-repository 'deb http://liveusb.info/multisystem/depot all main'
$ wget -q -O - http://liveusb.info/multisystem/depot/multisystem.asc | sudo apt-key add -
$ sudo apt-get update
$ sudo apt-get install multisystem