HxD is a Freeware hex, disk and memory editor, that is fast and can handle files of arbitrary size (up to 8 EiB).
Some of the feature highlights are:
Disk editor (automatically unmounts drives as necessary when saving changes)
Memory editor (full support for 64 and 32-bit)
Data folding, for easier overview and hiding inaccessible regions
Data inspector
Converts current data into many types, for editing and viewing
Open source plugin-framework to extend with new, custom type converters
Search and replace with support for various data types
Importing and exporting of Intel Hex, Motorola S-Records
Exporting to Pascal, C, Java, C#, VB.NET, PureBasic, but also HTML, RTF, and TeX
Checksum and hash generation and validation
File compare
Tools to split, join and shredder files
Currently, available in version 2.4 and 17 languages: HxD download.
P.S.: If you like it, please star the code on GitHub or give it a (good 😉) rating on download sites.