Cult classic PlayStation 2 game Okami got a Wii port. It never got a NES version, because that system was well before the game's time. But what if it did?
Website 72pins reckons that the game's 8-bit cartridge would look something like this. It also reckons that you can buy this mock-up for US$20.
Other what-if NES cartridges include God of War, Dead Space, and Shadow of the Colossus. Some, such as Halo and Katamari Damacy, are sold out.
Other cartridges, such as Sonic the Hedgehog and Resident Evil, are forthcoming.
The cartridges do not contain the actual NES versions of the game, but rather, a random playable NES title.
Don't let that stop you from playing NES Killzone -- in your head.