Rufus is a utility that helps format and create bootable USB flash drives, such as USB keys/pendrives, memory sticks, etc.

It can be especially useful for cases where:

You need to create USB installation media from bootable ISOs (Windows, Linux, UEFI, etc.)
You need to work on a system that doesn't have an OS installed.
You need to flash a BIOS or other firmware from DOS.
You want to run a low-level utility.

Despite its small size, Rufus provides everything you need!