There are various free tools that allows to create multiboot USB.
The big advantage is that you can use more than one ISO that can run from boot, for example install various Windows and Linux OS versions, or start an utility boot cd (eg. Hiren’s Boot CD).
Rufus – available also in portable version, multilanguage, UEFI and GPT support.
YUMI – was originally intended to be used to store and run various “LIVE Linux” Operating Systems and tools from USB. Using YUMI to install Linux from USB to a Hard Drive works on some but not all distributions. UEFI YUMI – Windows Beta version available.
Universal USB Installer – similar to YUMI, allows to run various Linux Live distributions.
XBOOT – supports many Linux Distributions and Utilities. Allows to choose which bootloader to use (Syslinux, Grub4dos).
SARDU – enables you to create a Multiboot UFD containing your basic essential Utilities, Antivirus, and Windows Installers.
WinSetupFromUSB – allows to install any Windows version, various Linux distributions and utilities. Supports UEFI.