This hex editor is a simple program that allows you to view and modify binary file data.
The license for the hex editor source code is public domain. This means that you can use it pretty much however you want and do not have to give me credit (although if you want to, feel free). The only thing you cannot do is claim legal ownership and prevent other people from using it.
Think of it like algebra. You can always use algebra however you want to solve problems, but you can't say that you own a patent on algebra and charge other people for using it.