Sonic the Hedgehog
The Sega Genesis had "add-on" systems that incorporated "Sonic" games. "Sonic CD", released for the Sega CD, was a 2D platform game released in 1993. The game introduced the characters Amy Rose and Metal Sonic and featured levels that differed depending upon whether Sonic was in the past, present, or future time frames. "Knuckles' Chaotix", a spin-off released in 1995 for the Sega 32X, featured Knuckles and a new group named Chaotix fighting against Dr. Robotnik. The game featured a two-player cooperative system in which the on-screen characters were connected by magic rings. There was also "Sonic Eraser", a puzzle game released exclusively on Sega Game Toshokan in 1991.
Sega Genesis
During his keynote speech at the 2006 Game Developers Conference, Nintendo president Satoru Iwata announced that Sega would make a number of Genesis/Mega Drive games available to download on the Wii's Virtual Console. There are select Sega Genesis games available on the Xbox 360 through Xbox Live Arcade, such as "Sonic the Hedgehog" and "Sonic 2", as well as games available via the PlayStation Network and Steam.