There may be instances where we need to modify the contents of a program to make it work properly, or validate a code behavior. Modifying data in a file can also change the code flow where conditional instructions may happen. Changing instructions can also work around anti-debugging tricks:

• HxD Hex Editor: A Windows binary file viewer and editor. You can use this to view the binary contents of a file.
• Bless: A Linux binary file viewer and editor.
• Notepad++: A Windows text editor, but can also read binary files, though reading binary files with hexadecimal digits would require a hex-editing plugin. Still, this is useful for reading and analyzing scripts, due to its wide range of supported languages, including Visual Basic and JavaScript.
• BEYE: A useful tool for viewing and editing any file type. BEYE is available for Windows and Linux. 
• HIEW: The feature that makes this software worthwhile is its ability to do on-the-fly encryption using assembly language.