Sega's Dreamcast died young, but its groundbreaking technologies paved the way for modern gaming. It was the first console with 128-bits. The first console with online gaming (Phantasy Star Online anyone?). And its memory cards, known as Visual Memory Units or VMUs, were basically tiny Game Boys.
Though the VMU as a portable device wasn't widely supported by developers (its puny processing power limited it to minigames like taking care of a Chao in Sonic Adventures or showing health stats in Resident Evil: Code Veronica), modders have given the tiny gadget new life as a retro console emulator.