Troy Denton and Brad Taylor made a USB reprogrammable NES cartridge:
Initially, Brad and I wanted to make a PCB that could do some very ambitious things, requiring either a very capable processor, or an FPGA device. We began down this path, but soon realized that we were biting off much more than we could chew for something we had never done before. So, we decided to take a step back, and make a smaller project to verify the foundations of our design. Our final design goals were:
*Be programmable via USB
*Be able to play NROM format games
*Feature nonvolatile storage (no battery required)
*Be as cheap and easy to manufacture as possible
Check out the video after the break.
Project info at troydenton.ca.