Boot Buddy allows you to easily create a bootable macOS USB installer on your Mac.
If you wish to create a bootable USB stick from Linux, WoeUSB might be the only tool you need.
If you don’t like burning CDs to create a bootable OS, then UNetbootin can help you as it lets you create live bootable USB drives from your ISO files.
If you want to create a bootable USB drive but with multiple operating systems, then YUMI is something that can help you do that on your Windows PC.
Etcher is a perfect app for those of you wanting to burn image files to SD cards and USB drives as the app lets you do just that really quickly with its three-stage process.
If you have always wanted multiple Linux distros on a single USB drive, then try out MultiBootUSB as it does exactly that.