Back in 2008 when the SD2IEC storage device came on the scene for the Commodore 64, it wasn't compatible with the .D64 disk image file format, instead it used what is refered to as the M2I format.  Here is a collection of games released by "znarF" that is in the old format.  Aparently based on this post over at the Nightfall Crew's web page, you need to convert these to P00 format to be used with newer SD2IEC firmware. 

For reference, this post on the Lemon64 forum is why I went hunting for this collection.

Update - You can go here to find the package in what I believe was it's original resting place and find a lot more information about M2I.

CBUS stands for Cartridge Back-Up System. CBUS I produces backup copies of cartridges for the Commodore 64. Using CBUS I saves wear and tear on ths Commodore 64  expansion connector by tricking the computer into running an image of the cartridge without having the cartridge physically present. Up to 17 cartridges can be stored on a single diskettae. With CBUS I, cartridges can be storad out of harms way rather than cluttering up the work area. CBUS I incorporates a RESET switch allowing you to perform a COLD Start without having to turn the machine off and on again. This permits study of cartridge object code, opening up the possibility of custom modifications.

I have one of these adapters and although it's not the 5.1 version, I figure someone else might benefit from the manual, so here it is.

Find much more info here.

The SaV64 is an over-voltage protection device for Commodore 8-Bit computers that require both 5VDC and 9VAC power sources. It monitors the 5VDC voItage level and automatically disconnects both the AC and DC from the computer when it rises above the trip voltage.

Note - This manual is from 2017 and came with batch 4 of this product.  Future versions may be different.

Lemon64 forum thread 

YouTube video

TRIANGULAR μOS is GUI (graphic user interface) operating system for 8-bit Commodore computers. This User’s Manual pertains to TRIANGULAR μOS 1.25/C64 version for Commodore 64.

Here's a link to the complete package (Software, Manual, Changelog)

Triangular uOS 1.25 for the Commodore 64, by Michael Goral, Released August, 2022.  Included in the archive is the operating system, full documentation and a complete change log.  See the extended description to see what's new in version 1.25

It's really amazing what has come out for our humble Commodore 64 over the years, and this piece of software is a good example.  Written entirely in BASIC, this is a complete OS!!!  It even has applications integrated.  I strongly recommend you check this out.  Here are some links to additional information / resources:

Lemon64 forum thread can be found here.

YouTube video can be found here.

This is a PDF version of the documentation for the 1541 Ultimate II, 1541 Ultimate II+ and the Ultimate 64 dated September 2022.  This documentation covers Firmware 3.10 / Core 1.41.

CCGMS Future v0.1 - Released in August 2021 by Mist64 is the next step in evolution for the beloved CCGMS terminal program originally written by Craig Smith, then later updated by Alwyz. New features include:

CCGMS Future v0.2 - Released in March 2022 by Mist64 is the next step in evolution for the beloved CCGMS terminal program originally written by Craig Smith, then later updated by Alwyz and Michael Steil.  New features include:

A CBM BASIC Editor for Windows written by Björg Stojalowski in VB.NET 2010

V1.4.7
======
- tried to fix probs with things auto-selecting via the mouse when maximising window or loading new files
- repaired issue of Shift+F3 search not scrolling down screen sufficiently to display next found item

A CBM BASIC Editor for Windows written by Björg Stojalowski in VB.NET 2010

V1.4.6
======
- Attempted to add abbreviated token support (see "TokenList_BasicV2_ed.txt")
- Added keymap for suit WinVICE on Swedish keyboard (see "KeyMap_Swe_WinVICE.txt")
- Added "Cut Block", "Copy Block" and "Paste Block" menu items triggering on CTRL+Shift+X, CTRL+Shift+C and CTRL+Shift+V, respectively.
- Ctrl+Shift normally toggles between the upper & lowercase charsets, but I've disabled this behaviour if you use the right-hand-side CTRL key.
- Added in Schlowski's fix relating to a ctrl-left/ctrl-right issue of the display going out-of-sync and showing a lot of spaces before the first character.
- Fixed a prob when moving down from the end of a long-line to a short line, if you did a ctrl-left, it would get an exception due to trying to perform a .substring() on a shorter string.

Fast Hack'Em v9.9a (Mike J. Henry / Basement Boys) - Fixed, patched and updated by Joe Bunt, 2022. 

It's pretty amazing the lengths our fellow Commodore(ian) went through to fix issues and bugs from various versions of Fast Hack'Em, to finally put together this version which is believed to be bug free.  Please check out the extended description to see Joe's comments about the process and updates he's applied.

AutoClock v1.6 is a GEOS Auto-Exec utility that can set the time and date on boot-up.  It works with both the Commodore 64 and 128 versions of GEOS.  Back in 1991 when Rick Koch wrote this, there was a bug that caused the text in the box to get cut off when used on the Commodore 128 in 80 Column mode.  Bruce Thomas fixed this positioning error back in October 2021, but just today made one last tweak that now lets it properly save the date when used with the new version number.  

In the archive are both a GEOS format program and one in CONVERT format.

I found this nicely formatted and concise guide to Merlin 128 while looking through other goodies at the Bombjack site.  I highly recommend you go visit, that's the place to find books, guides, manuals and all sorts of other great retro related stuff.

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 any personal computer.

This firmware update (v1.6.1) is applicable to THEC64, THEC64 Mini and THEVIC20.

Features introduced in version 1.6.1

• [All models] Adds Commodore 1351 mouse support to the C64
• [All models] Adds support for up to four joysticks
• [All models] Adds support for THEMOUSE
• [All models] Adds support for THEGAMEPAD
• [All models] Adds a new game Space Lords, a multi-player game that utilises the new mouse and multi-joystick support

Northcastle Structured BASIC v1.7 by Mike Roche (June 1984) - This is very similar to Waterloo BASIC, in fact it will run most programs written for Waterloo. I found a nice article about this language in issue 23 of TPUG Magazine (May 1986).  Included on the disk is several versions that can be loaded into different parts of memory so it can co-exist with other utilities.  There is also instructions, source code (written in PAL assembler) and several sample programs.  I would consider this a complete package.

This is an unofficial release of CP/M for the Commodore 128 on a .d71 disk image that I found over at the H2Obsession website.  This version is the last official release from Commodore with a Y2K patch.  Please visit the H2Obsession site for more information and possibly a newer version

I found this rather obscure BBS program for the Commodore 64, written back in 1986 by Charles Van Lingen, while rooting around archive.org.  Although the program disk is labeled as v4e, the program itself shows v4c as you can see from the screen shots.  The program is mostly written in BASIC, so it's highly customizable and might be useful for learning purposes.  One thing to note as pointed out in the archive.org posting is that there is likely a backdoor in the system that allows the bypassing of passwords.

Here is a link to the Toronto CBM mailing list from the peson who uploaded this to archive.org.  There is some additional information in the thread you might find interesting.

The Magic Candle is a game with many features and options. As you progress, you will need to read the "Sage Advice" later in this book. The advisers of King Rebnard will provide your hero with information he must know.

You should get a feel for the game before you seriously attempt to take care of the problem of the magic candle. Follow these directions for a quick start. Later, you may decide to start over. But, first, go through this process to become familiar with the game system.

This release of Lisp 64p V4 by "Hamster" is a fixed version of the original, released in the German magazine Input64 dated April 1986.

Lisp 128 Release 1.00 for the Commodore 128 - Included in the archive is the source code, binaries (on .d64 floppy image) and documentation (in German).

Lisp is the second-oldest high-level programming language still in common use. Only Fortran is older, by one year.

Here are two bootable CP/M System disk images for the Commodore 128.  One image is a .d64 and will need to be used with a 1571 floppy drive (won't work with a 1541) and the other is a .d81 for use with a 1581 floppy drive.  Although the screen shots show this as CP/M 3.0, it is interesting to note that there is actually no such thing, and this is actually CP/M Plus 3.1.  If you're interested in details about this and CP/M history, check out this link over at H2Obsession.  For other CP/M System disks, check out the Zimmer File Archive.

This is a recreation of the CP/M Kit Companion Disk that came with the book "CP/M Kit for the Commodore 128". Included in this archive are two .d81 floppy disk images and the book in PDF format. One disk image contains a bootable CP/M 3.0 System Disk and the other is a .d81 floppy disk image of the CP/M Kit Companion Disk.  See the associated screenshots for listings of the contents on both disks.

I found this disk image on archive.org, and while doing some research, also found this thread on Lemon64.  Here is a link to the book elsewhere on this site.

CCS64 v3.9.3 (Released Nov. 15, 2021) is a Commodore 64 emulator for Windows 7 / 8 / 10.  The only information I've seen on the difference between this version and the last one (v3.9.2) is that it now fully supports Windows 10.