UltraEdit is the world's best text editor for Windows, Mac, and Linux.

wxMEdit is a cross-platform Text/Hex Editor written in C++ & wxWidgets. wxMEdit is an improved version of MadEdit which has been discontinued.

Binary Ninja is a reverse engineering platform.

wxHexEditor is an open source cross-platform hex editor written in C++ and wxWidgets. It can work as low-level disk editor too.

010 Editor is a text editor.