Whether you harbor fond memories of the Nintendo 64 or despise its baffling controller and chunky, untextured polygons, one thing everyone can agree on is that the system was not very portable. At least, until a hacker calling his or herself "Bungle" got a hold of the machine.
According to a description Bungle wrote on the Bacman retro console modding forums, this modified Nintendo 64 features support for both Expansion and Rumble Packs, custom buttons, a legitimate N64 analog stick, internal memory and a 3.5" screen. As you can see, it accepts actual cartridges, and Bungle claims that the device's 4400mAh battery offers about four hours of juice. That's not quite on par with the Nintendo 3DS or Sony's Vita handheld, but is respectable for hardware that was never intended to fit in your pocket.
Best of all, this isn't some hyper-rare one-off project. Bungle claims that this is the fourth such device he or she has created to date, and that more are on the way. It's unknown if these things will ever be available for purchase, but we're keeping our fingers crossed.