Fmon is a RAM based machine code monitor for both the BBC and Acorn Electron. It is relocatable to any part of RAM the user desires and occupies 5.5K of memory.
All the usual commands one expects from a monitor are available such as block move, dissassembly, hex and ASCII dumps and searching through RAM or ROM areas.
Memory locations may be changed and searches performed. Also included is a line by line assembler and a relocator program.
There is the facility to single step through machine code programs and stop at any of the user-defined breakpoints. Up to 127 breakpoints can be set without having to alter the program being traced, thus making the tracing of ROMs no problem.
I am no ace machine code programmer, but I found Fmon had all the facilities of a monitor that I require and a great deal more. It is very straightforward to use and extremely well documented. My only quibble is that it resides in RAM rather than ROM which the monitor I normally use does.