These monitors have been OCRed or typed in from the manufacturers original documentation. In the case of the Intel monitors, they all contain common code. You can see the development through the many years of monitors!
A lot of this work was driven by Herb Johnson placing ROM images on his Intel MON-80 PROMs page.
I have written tools to help me generate source code from .HEX and .BIN files of old monitors. Here are those tools:
Herb Johnson wrote the HEX2BIN routine.
The current version of the 80XX assemblers is n1.0d. This version adds in the MODULE pseudo op discussed in the monitors section.
There are two 8008 assemblers here: asm8008 handles the 1975 nemonics, asm8008a handles the earlier 1972 mnemonics.Assemblers for 8008/8048/8051/8080/8085 Monitors
I have OCRed and edited several Intel monitors. Also included are monitors from other manufacturers of CPU boards. I have also reverse engineered monitors from .HEX or .BIN files and from actual ROMs.
Some of these monitors use a new assembler pseudo op "MODULE" which produces hexadecimal or binary files with the starting hexadecimal address appended to the name. This allows Monitor programs to be broken across EPROMs at a byte level.
MDS I Version 2.0 is still a work in progress! There are assembler errors for references outside the ROM address space. The monitor contains calls to additional commands which are contained in i35.asm and i60.asm.Mon80 Ver 2.0 for Intellec 8/Mod 80 
The rest of these Intel monitors are complete, as far as I know. They assemble with my assembler above and have been verified against either the source document or the binary file.Mon80 Ver 3.0 for Intellec 8/Mod 80 [14 Apr 1975]
This is a new monitor for the MDS-225 which adds more functionality and removes all the code to support the IOC board. This has been extensively tested on the MDS-225 CPU board.My Mon80 Ver 1.0 for MDS II [15 Jul 2015]
These are monitors I have found from other Intel vendors.SSM 8080 Monitor Ver 1.0 
These are monitors I have found from Z80 vendors.SSM Monitor
I have OCRed and edited the PLM-86 file for the SDK-86 monitor. This monitor will build with the PLM-86 tools for DOS.SDK-86 monitor
I disassembled this monitor from a ROM image I had. The original source code is in the MUMON88.A86 file. This monitor I used in PCs and on the MPX-16 that I built in 1983.
Here is the first monitor I wrote for the M6800 in 1976. I have ported it to many other microprocessors over the years. This version was ported to a M6800 CP/M-80 simulator I wrote in 1983.My Original 6800 Monitor
These are monitors I have found from Motorola and other M6800 vendors.Altair 680b Monitor (ASCII)[Unknown]
These are monitors I have found from Motorola and other M6809 vendors.SWTPC 6809 DiskBug0 Ver 3.5 [27 Aug 1980]
Last Updated: 15 Jun 2015