Hex Fiend is a fast, clever, and free Hex editor that has many unique features:

• Insert, delete, rearrange: Hex Fiend does not limit you to in-place changes like some hex editors.
• Work with huge files: Hex Fiend can handle as big a file as you're able to create. It's been tested on files as large as 118 GB.
• Small footprint: Hex Fiend does not keep your files in memory. You won't dread launching or working with Hex Fiend even on low-RAM machines.
• Fast: Open a huge file, scroll around, copy and paste, all instantly. Find what you're looking for with fast searching.
• Binary diff: Hex Fiend can show the differences between files, taking into account insertions or deletions.
• Smart saving: Hex Fiend knows not to waste time overwriting the parts of your files that haven't changed, and never needs temporary disk space.
• Data inspector: Interpret data as integer or floating point, signed or unsigned, big or little endian...
• Embeddable: It's really easy to incorporate Hex Fiend's hex or data views into your app. Its permissive BSD-style license won't burden you.