The Turbo Master CPU was an early CPU accelerator for the Commodore 64 and quite probably the first to have commercial success. It predated the Super CPU by several years. It came in two versions one with JiffyDOS and one without. RUN Magazine featured an in-depth article about the accelerator.
Special provision was made to ensure that the accelerator was fully compatible with GEOS, including the RAM expansion unit Geo RAM.
 
From facebook:
I am soliciting for help to finish this long incomplete project to reverse engineer the Schnedler Systems TurboMaster 4MHz CPU Accelerator Cartridge. I've mapped out the schematic, created a PCB, hand aligned the PCB with the original artwork, and run a few of the boards, but even when I place the ICs from a known working TM, I cnanot boot from the PCB (it *almost* boots, as it comes up with the CYAN/BLUE colors, but no intro screen and no cursor). I have placed all of my files in github, and I'm hoping someone can spot an error that I am making with this reverse engineering effort. I have created some Paint.NET files I am using to manually go through the PCB versus the original artwork, which I can also upload, but I have not yet found a problem (though there must be one). I believe I have also determined the equations in 2 of the 4 PALs (and Thomas Christoph I believe has a third). If I can get the PCB sorted, I can focus attention on the last PAL (I probably cna brute force it by looking at the schematic, if I know it's correct), and converting the known equations back into CUPL so folks can make their own PAL/GAL replacements. The goal, obviously, is to learn how this unit works, so I can create an 8MHz version, and then see if I can use that as a base for the SuperCPU (or at least learn enough to move that long dreamed project along). 

If you can help please contact RETRO Innovations and help make this project a reality!