It aparrently lets you use your Amiga as a C64 disk drive. I have never tried it, but it looks like you need to build a circut to connect the Amiga's parallel port to the C64's serial port. Think I'll just get the MMC64 instead. Does anyone know whether I will be able to use the Prophet64 connected to the MC64 passthrough, and whether I can save Prophet64 projects to the MMC card?
Please note that the MMC64 does not allow you to load multifile games (e.g. from D64-files). However, you can start single Programs (.PRG-files), look inside D64-images and start PRGs from there, write back D64-images to your 1541, convert 1541-disks to D64, isten to WAV-files, watch ANIms and pictures, play SIDs and many many other things.
If you also have a Retro Replay, you can make full use of the "Dreamload" plugin, which allows you to also load multifile D64/D71 images. The IDE64-fixed version work fine with it.
I don't know about the Prophet64, but the Retro Replay works fine together with the MMC64.