AECM lets you create cartridge images directly on your Amiga compatible
computers. Simply add the files and save a .crt image. You can even save the
.crt image directly to a d64 for easy writing with your Catweasel card (or any
other .d64 solution)

Working:
create a new cart
add/remove files
save cart image (.crt)
embed cart image in a .d64 file

To do:
Screensaver/splashscreen cart options
Cart auto-sort toggle
Reload carts for editing