Bless is a binary (hex) editor, a program that enables you to edit files as
a sequence of bytes. It is written in C# and uses the Gtk# bindings for the 
GTK+ toolkit.

Main Features
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  * Efficient editing of large data files. 
  * Multilevel undo - redo operations.
  * Customizable data views.
  * Fast data rendering on screen.

WWW: http://home.gna.org/bless/