Build a Game Boy Emulator

You build an emulator that implements the Game Boy's Sharp LR35902 CPU instruction set, its memory map and cartridge bank switching, timers and interrupts, and a pixel-processing unit that renders backgrounds, the window, and sprites scanline by scanline until real games boot and play. It is worth building because hardware emulation demands ruthless accuracy: a single mis-decoded opcode or wrong cycle count shows up as a crashed ROM or a corrupted screen, so it trains a debugging discipline most projects never require. It is resume-defining because emulators are concrete, demoable proof of low-level mastery — you can literally show Tetris running on software you wrote from a hardware spec. The combination of CPU dispatch, cycle-accurate timing, and graphics rendering covers a remarkable amount of systems knowledge in one project.