hexedit is your typical standard hexadecimal editor that you would ever need.
hexedit 1.2.12 (2005-09), with --color
Click to watch some usages
It doesnt have any fancy UI, but it gets the job done. You can copy, paste, edit, truncate, search, etc.
I have been using it for six years, the same code is more than a decade code. Even the latest code is available for almost three years, I just dont feel the need of updating it.
hexedit was created by Pascal Rigaux on 1998-07-21, written in C under GPLv2, latest version is 1.2.13 (2013-03-01).