That tool is Easy2Boot, and don't let the janky UI put you off because you will want to learn what it can do. My only suggestion is to get a large USB drive to use with it, since you will want to fit ...

You know you’ve got a serious PC problem when your computer refuses to get through even the first phase of startup properly. If you can't get into Windows or macOS at all, then your troubleshooting ...

I've got a 4 Gigabyte flash drive that I'd like to make bootable. For right now, I need it to boot DOS or DS linux. I'd like to have it boot to grub or something similar so I can select either one.