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.
What's new in Hex Fiend
Note: Now requires OS X 10.9 or later
Added basic extended attributes support. The open file dialog will now list the extended attributes for the selected file. This allows opening classic metadata such as resource forks ("com.apple.ResourceFork") and Finder Info ("com.apple.FinderInfo"), and other data (for example "com.apple.quarantine"). Currently extended attributes are read-only and cannot be modified.
Data Inspector can now view half-precision (2-byte) floats.
Prevent the document from being modified when editing ends with the data inspector.