wxHexEditor is an open source cross-platform disk/sector/file hex editor written in C++ with a wxWidgets-based user interface.
The project seems no longer developed since 2020. Last version, 0.24, released in December 2017, can be still downloaded from SourceForge and GitHub
VBinDiff (Visual Binary Diff) displays files in hexadecimal and ASCII (or EBCDIC). It can also display two files at once, and highlight the differences between them.