Ms Mad Lemon has just demo’d two “rom cart” options for the Atari 800 PC: The SIO2SD that plugs into the serial port and the Ultimate Atari Cartridge, which plugs into the cartridge port:
SIO2SD (other components required, check page): https://lotharek.pl/productdetail.php?id=58
Ultimate Atari Cartridge Github: https://github.com/robinhedwards/UltimateCart
Ultimate Atari Cartridge Purchase: https://thebrewingacademy.com/products/atari-800-xl-xe-ultimate-sd-cart
Incognito Board: https://lotharek.pl/productdetail.php?id=275
I’ve personally never used an Atari 800 PC, but had a CoCo2 as a kid and was always curious about other computers in a similar form factor. Lucky for us, there’s some quality YouTube channels out there that let us experience these things without having to purchase them all ourselves!
Update 12/13: A follow-up video was just posted that shows installation of the Incognito board, also for the Atari 800, linked below.
Also, fans of classic PC’s might argue that calling these “ROM carts” would be inaccurate, as they load images of cassette tapes and floppy disks as well as cartridge roms. Regardless of what you call it, check out the video if you’d like more info on how both of these work, as well as a demo of the incredible fart sound one of them makes when (presumably) trying to emulate the sound of a floppy disk drive.