HxD is a freeware hex editor, a tool that can open and edit computer code. In the right hands, it's a powerful utility that can inspect, compare, and verify files, disks, disk images, memory, and log files; patch errors, and repair disk structures.
Pros

Really big data: HxD's current version handles large data sets. If it fits on a disk, HxD can open it -- fast search and replace functions, too.
Standard options: HxD packs lots of useful extras, like a checksum generator, multiple charset support, RAM editor, ghost caret, file shredder, splitting and joining, unlimited undo, and a portable version.
Export data: HxD exports data to source code (C, C#, Java, Pascal, and VB.NET) or to hex formats.
Cons

Not for the inexperienced user: This isn't a flaw in the tool; it's just worth noting that this is geared toward advanced users.
Bottom Line

With an attractive, efficient interface and an extensive menu of powerful tools and extras, HxD delivers the goods. And if you need a feature that HxD doesn't have, the developer wants to know about it. Coders, system administrators, and advanced users will want HxD in their toolkits.
Publisher's Description

From Mael Horz:
HxD Hex Editor provides tools to inspect and edit files, main memory, disks/disk images and their structure, using a simple and modern interface. You can employ it to analyze big log files, patch ROM files for emulators, repair disk structures, validate data or search for game cheats. Features of HxD include efficient handling of huge files, fast and flexible search & replace, file comparison, checksum & hash generation, exporting to several formats (source code, formatted output like HTML, hex files for EEPROM programming), a file shredder, a file splitter/joiner, and graphical statistics.
What's new in this version: Version 1.7.7 is a bug fixing release.