For the C64, C128 (in 40-column mode), and VIC-20, the BackBit cartridge is for sale at
https://www.backbit.io/As developer Evie Salomon says, "It's a multi-function cartridge that operates with a Micro-SD card."
See Evie's introduction to the BackBit at
https://www.youtube.com/watch?list=PLik3CBZlL5eW3O-LaLSmVX5k3eL0nKWet&v=G3t2_iloGVQ&feature=emb_logoand how to use the BackBit at
https://www.youtube.com/watch?v=8YKruh_DiEY&list=PLik3CBZlL5eW3O-LaLSmVX5k3eL0nKWet&index=2The big selling point of the cartridge is its compatibility with various disk, tape, and cartridge images, like D64, D81, CRT, PRG, P00, .20, .40, .60, .a0, and more. Just drop the image(s) onto a microSD card and pop the card into the BackBit. You see the file(s) on a menu, you select the one you want, and it loads and runs. No Commodore calisthenics to get the computer to recognize the image type.
As mentioned above, the BackBit cartridge works with the VIC-20 with a special adapter that fits the BackBit into the adapter. Evie has a video that explains it at
https://www.youtube.com/watch?v=Une9mquKL0w&list=PLik3CBZlL5eW3O-LaLSmVX5k3eL0nKWet&index=7For an independent review of the BackBit, go to
https://enragedgeeks.blogspot.com/2020/01/normal-0-false-false-false-en-us-x-none.html Writing from Sydney, Australia, at the moment,
Robert Bernardo
Fresno Commodore User Group -
http://www.dickestel.com/fcug.htm April 25-26 Commodore Los Angeles Super Show -
http://www.portcommodore.com/classP.S. Evie Salomon is tentatively scheduled to appear at the April 25-26 Commodore Los Angeles Super Show.