If you've never come across one of the Magic Eye books, then the picture above might just look like a random collection of dots. But if you know how to squint at it just right—and go cross-eyed in the process—then a familiar scene from DOOM will present itself in 3D, with the gun model at the bottom of the image and two pillars in the distance (at least, that's what my unpracticed eyes see).
That's what you get in OMDO, which is identical to DOOM except every frame is a random dot autostereogram (like the one above). Some people prefer going cross-eyed to see them in 3D, while some prefer going wall-eyed—OMDO caters for both by letting you switch between parallel convergence and cross-eyed convergence from the main menu.
Again, if you've never tried to look at one of these pictures before, then you're going to be lost. But once you know how to view them, you'll never forget. This Wikipedia page summarises a few techniques, and there are plenty of other guides out there.
It helps to have some familiarity with DOOM's maps, according to creator blogum, and I imagine that after five minutes your eyes might go a bit wobbly, so it's probably best to play in short spurts. But as somebody that loved the Magic Eye books as a kid, I'm definitely going to give it a whirl.
Head over to itch.io to download it.