Cxmon is an interactive command-driven file manipulation tool that is 
inspired by the "Amiga Monitor".

Cxmon has commands and features similar to a machine code 
monitor/debugger, built-in PowerPC, 680x0, 80x86, 6502 and Z80
disassemblers and special support for disassembling MacOS code.

You can also simply use it as an interactive workbench for manipulating 
files, or even as a hex calculator.

WWW: http://cxmon.cebix.net/