Whoa! This is a website with tons of ATR disk images with games. http://www.mushca.com/f/atari/index.php?idx=1

Ok, a week passed and I haven't been at home but what I'll do for this is take a few pictures and post them and write up my thoughts on some games that work. It seems like it will be a nice way if I want to try out one 800 game.

It does! It does a great job. I have more I want to say about this cart this week.

Does the MiSTer do Atari 800? I've never looked. I don't think I've played any Atari computers on it yet.

I can't find a pre-existing thread, so here we go:

Years ago I bought the Atari 800XL "Sdrive2" (squared, not 2) cart. It plays ... disk images. It's batting maybe .300.

This is a video of it: https://www.youtube.com/watch?v=0oI0ZOdIpWw
This is a PDF with instructions: https://github.com/fintros/SDrive-ARM/blob/master/docs/Orig_SDrive_en.pdf
This is where people are talking about how they can't get it to work on Atari Age: https://atariage.com/forums/topic/262509-sdrive-arm-preorder/#comments