ResKnife is a resource editor for the Macintosh. It supĀports resource files in any named fork (data, resource or one of your choosing), runs natively on Mac OS X, as well as classic Mac OS, and allows editing the data fork using any of its editors.
HexEdit is a hexadecimal file editor for the Macintosh. The most widely used editor of its kind on the platform, HexEdit can handle file sizes of up to four gigabytes with ease, yet has memory requirements of less than a megabyte (with colour turned off).
HexFiend, the brilliant hex editor capable of editing gigantic files with ease, has been revised to version 1.1.1 and released as an open source program. Some of you remember tweaking things in hex with ResEdit in the bad old days.