Hex Editor
Editing file in binary format (hex mode).
All Platforms
HexEd.it
A full-featured hex editor that runs in your web browser using HTML5/JavaScript technology.
Support Platform: Web Application
Price: Free
User Interface: GUI
Links: Website
ImHex
ImHex is an open-source hex editor suitable for reverse engineers and programmers.
Support Platform: Windows
, macOS
, Linux
Price: Free, Open Source
User Interface: GUI
Links: Website
VSCode + Plugin
Using VS Code + HexEditor Plugin can achieve hexadecimal editing.
Support Platform: macOS
, Windows
, Linux
Price: Free
User Interface: GUI
Links: VS Code Marketplace
UltraEdit

UltraEdit is a well-established text editor and also a hexadecimal editor.
Support Platform: macOS
, Windows
, Linux
Price: Paid
User Interface: GUI
Links: Website
macOS
Hex Fiend

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.
Support Platform: macOS
Price: Free
User Interface: GUI
Links: App store
Windows
HxD
HxD is a reeware Hex Editor and Disk Editor. It is a carefully designed and fast hex editor which, additionally to raw disk editing and modifying of main memory (RAM), handles files of any size. The easy to use interface offers features such as searching and replacing, exporting, checksums/digests, insertion of byte patterns, a file shredder, concatenation or splitting of files, statistics and much more.
Support Platform: Windows
Price: Free
User Interface: GUI
Links: Website