This patcher is just plain COOL!  Basically what it does is let you patch a legally owned JiffyDOS ROM image to add several new features.  Once you've applied the patch to create a new ROM, you can use that ROM with something like an EasyFlash 3, Ultimate 1541 or Turbo Chameleon to make it your Commodore 64's default Kernel. This really is a must have for JiffyDOS owners. 

See the detailed description for additional information on the features of this patcher.  Here is a link directly to the source - http://blog.worldofjani.com/?p=3544

JaffyDOS is a custom kernal for the C64/SX64 with enhancements for SD2IEC.
Filebrowser and Kernal modifications by: jani@worldofjani.com

This archive contains a Word document with an extremely well documented disassembly of JiffyDOS v6.01.  Credit for this work goes to Magnus Nyman.