MMC Replay - MMC64 and Retro Replay combined in one cartridge, with some improvements
Micromys - An adapter that allows connecting PS/2 compatible mice (including wheel-support) to c64 and Amiga joystick-ports (and all other computers that share the same pin-configuration).
Amiga Clockport compatible addons for MMC64, Retro Replay and MMC Replay:
RRnet: A c64-compatible Network-Interface. Comes in 2 shapes, the old long RRnet fits Retro Replay and MMC64 (though partly blocking the latter's passthrough expansionport), the new L-shaped RRnet2 fits MMC64 and MMC Replay and was built with MMC Replay in mind.
Silver Surfer: Highspeed RS232 Interface for the c64. Fits onto Retro Replay, MMC64/Replay compatibility unknown.
mp3@c64: hardware mp3 decoding from SD card. Made for MMC64, Retro Replay and MMC Replay compatibility unnkown.
Keyrah - An interface that allows the connection of Commodore keyboards to USB-capable computers