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WiiWare is a service offered by Nintendo for Wii owners. It is similar to the Virtual Console, however deals in completely original pieces of software similar to Xbox Live Arcade or the PlayStation Network.
Sega has only released three games for WiiWare, Sonic the Hedgehog 4: Episode I, Let's Catch and Chindouchuu! Pole no Daibouken, preferring to support rival consoles presumably due to a 40MB limit placed upon developers.