Pico CAD is a full low poly modeling tool in Pico 8. It's very different from an implementation standpoint than SpriteStack, which is voxel editor, rather than a polygon modeler. They are only similar in both being low resolution, resulting in a similar aesthetic.

FYI - SpriteStack has a direct support for PicoCAD files (without need to convert them to anything else) - https://twitter.com/rezoner/status/1412759115370307584

I have so many questions. The only thing I know about pico8 is it's a VM for very low end hardware, it used a hexidecimal numpad as it's interface, and black and white.

I just ran the download from the website and it's so much more than that. Are there any other resources to learn more about this?

What you're thinking of is CHIP-8[1]. PICO-8[2] is similar in spirit, though much more powerful. It's a constrained (in memory, code size, and cpu cycles) lua environment tied to a 128x128 16 color display.

[1] https://en.wikipedia.org/wiki/CHIP-8

[2] https://www.lexaloffle.com/pico-8.php