HexEdit

A freeware hex editing utility for the Macintosh, originally by Jim Bumgardner. It was released in 1991, when such utilities for the Macintosh were hard to come by.

It was meant to be used principally as a diagnostic aid for programmers, but is also sometimes used to crack Mac software.

The current version is maintained by Lane Roathe.

There are hex editing programs, including programs with that very name, available for most operating systems and computers. Some of these programs edit system memory in hexadecimal (hex), some edit files, and some do both. I just did a quick search in Google and found:

• HexEdit for Unix at http://www.chez.com/prigaux/hexedit.html
• HexEdit for Macintosh at http://freespace.virgin.net/nick.shanks/mac/noframes/hexedit.html
• HexEdit for Windows at http://members.tripod.com/AndrewPhillips/

...and there are many more.

Minimalists can use DOS DEBUG, while those with (somebody else's) money to blow can buy Symantec's Norton Utilities. A high-powered programmer's editor like Visual Slick Edit will also edit files in hex, as an option.