Easy Flash 3
First of all you can have EIGHT custom Kernals. I used this for my JiffyDOS, until I bought the actual chips and install them into my C64, that alone is pretty amazing.
THEN you can add Action Replay and Super Snapshot to this. There are three buttons on the end of this cartridge for MENU, Special and RESET. Special is used for the Snapshots.
This is the BOOT MENU.
The third section is for cartridge images (CRT) that you can add to the Easy Flash 3. You have seven slots, BUT that does not mean that you can only have even programs. You can combine dozens and dozens of programs into ONE CRT file.
I use NDEFGUI to do this.