FAST/128 Software Development System by L. Boere.  Unfortunately I can't remember where I got this and there is no additional documentation on the floppy image.  It appears to be an Assembler and that's about all I can tell you.  If you have further information, please drop me a line.

LADS 123 Assembler is the programming environment used for the book "128 Machine Language Programming for Beginners".  Nothing fancy here, but handy if you're going through the book mentioned.

• Link to book

Merlin 128 is an extremely powerful, comprehensive Macro Assembler system for the Commodore 128 computer. It consists of four main modules and numerous auxiliary and utility programs which comprise one of the most complete assembler systems available for anypersonal computer.

You can find the Merlin 128 manual here.

MIDNIGHT ASSEMBLY SYSTEM by Matthew Montchalin is an assembly language development package for the Commodore 128 that supports the 17xx RAM Expansion units.  Here is some info I found on how to load and run the program, but I am unable to find any other documentation.  If you have the manual or docs and would like to share, please reach out via the "Contact Us" button on the menu bar.

• Executes from either Bank 0 or Bank 1 and generates code into the Bank that is opposite the one that it resides in.
• Supports the Commdore 1750 REU with its own built-in RAMDOS, complete with commands for automatically transferring entrire batches of files to and from the 1750 REU.
• How to Load MAS into Bank 1: BLOAD"MAS-128 W*",B1
• Then execute it by typing: BANK 1 : SYS 5888
• To restore the screen editor, press CTRL + RESTORE simultaneously.
• To remove offending tab settings, press CTRL + L at the appropriate place.
• To establish new tab settings, press CTRL + K at the appropriate pave.
• For a Cold RESET, press ESC + RESTORE.

Robs Syms by Rob Knop is a collection of Equates and Macros for use with the Merlin 128 assembler.  Here is the text from the readme file on the disk:

This archive has six files: robsequs.s, robsmacs.s, robsjsr.s, robsequs.asm, robsmacs.asm, and robsjsr.asm. The .s files are Merlin files (readable by the Merlin editor), the first two of which I include in most  everything I write (with Merlin's PUT command). The .asm files are also Merlin code, but converted to a format readable by a normal text editor such as ZED.

They are archived and distributed so that people can understand any other Merlin source that I distribute! :)

Notes on robsequs: this file contains a stack of useful equates. Mostly it is Kernal routines and zero page equates, although a few MMU registers and other random stuff is thrown in. A note about the zero page equates: a glance at the file will show that I am a GEOS programmer at heart. The zero page pseudoregisters are very reminiscent of r0, r1, ... from geosSymbols. These zero page registers are all in zero page space used by BASIC but not by the Kernal. Thus, using these registers is not possible with a ML program that needs to interface with BASIC (unless you are very careful and/or muck around with the MMU register $d507 to move zero page around).

Notes on robsmacs: Macros for use in Merlin. You will notice that most of them are straight out of geosMacros. Yup, I'm a GEOS programmer who grew addicted to the geoProgrammer macros!

Notes on robsjsr: This is a little JSRFAR sort of routine that resides in zero page. It has the advantage over the usual 128 JSRFAR that it returns to the bank from whence it was called (whereas the usual 128 JSRFAR always returns to Bank 15). The comments describe it fairly well, I think.

MONITOR add-on for assembling and disassembling Z80 mnemonics. Use BLOAD and SYS DEC("2D00") to activate. The new MONITOR command "Z" disassembles in Z80 mnemonics (preceded by a dot), and "*" assembles in Z80 mnemonics.