Indeed, and even then, there's some sw-hw-codesign stuff that kinda helps you do what PCIem does but it's usually really pricey; so I kinda thought it'd be a good thing to have for free.

PCIe prototyping is usually not something super straightforward if you don't want to pay hefty sums IME.

The "DMA cards" used for video game cheating are generic PCIe cards and (at least the one I got) comes with open documentation (schematics, example projects etc).