Hexinator is a full-featured hex editor that allows to edit files of unlimited size.
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Pro Basic hex editing features are free
Hexinator has some advanced reverse engineering features. You can create a "grammar" for custom binary file formats and let software parse files automatically.
A portable version is available.
Pro Automatic file decoding
Hexinator decodes various file formats automatically with "grammars". There are already many grammars for dozens of file formats.
Pro Scripting engine
Allows scripting with Lua or Python (Paid version only).
The highlighting is in paid version after the trial period, and 80$ is not an attractive price.