SD2IEC is a hardware mass storage device using an SD/MMC card and interfacing with the Commodore IEC bus. It is based on the ATmega644 micro-controller from the Atmel AVR micro-controller family. The most prominent use of SD2IEC is emulation/replacement of a Commodore-1541 disk drive for a C64.
My board was made by a guy called ‘Charlie’. Its a brilliant little device!
Its very easy to use. You can copy either PRG files or D64 disk images. I’ve not found a single D64 disk image file that hasn’t worked. I’ve tested it on my C64 and my C128 which has JiffyDOS installed. Its so much quicker on the C128 in JiffyDOS mode.
There is more info about the device at C64-Wiki.