My senior project was a Super Nintendo emulator. It worked out well because 1) there's a decent amount of documentation out there on sites like romhacking.net,

My senior project was a Super Nintendo emulator. It worked out well because 1) there's a decent amount of documentation out there on sites like romhacking.net, 2) there's usually at least one open-source emulator that you can use to figure out tricky bits (we used bsnes to help us understand how to render graphics when the documentation was vague or incorrect), and 3) emulators are super-easy to demo and verifying if you got it right is easy due to existing code you can run to test.