Known as the Mega-CD outside of America. The Sega CD was an expansion module for the Sega Genesis home console. it allowed for long games, enabling role-playng games which had been PC-only, to enter the home console for the first time. Games could now be made with higher quality graphics and more levels included. No more need to compress games to fit them on a limited space ROM cartridge. No more reducing image quality, sound fidelity, and removal of entire levels. The new controller bumped the button count from 4 to 6, allowing for games that could not have previously existed. The Sega CD was actually successful and ended up with plenty of games over what was a very respectable lifespan for what was actually an expansion module. No one in the videogame-industry would know it at the time, but console expansion modules would almost never succeed ever again.
Below is the videogame library for browsing at random.
'Mary Shelley's Frankenstein'
A-Rank Thunder Tanjouhen
(National Football League) Football Trivia
'Eternal Champions: Challenge from the Dark Side'
'3 Ninjas Kick Back'
Game no Kanzume: volume 2
'(Make My Video) inxs'
'Joe Montana's Football'
Sherlock Holmes: Consulting Detective
Mad Dog-2: The Lost Gold
'Brutal: Paws of the Fury'
'Ecco: The Tides of Time'
Nostalgia 1907 (in North American Sea)
Chuck Rock: 2 - Son of Chuck
Ranma half Byakuran Aika
'Sega Classics: Arcade Collection'
Road Avenger (AKA Road Blaster FX)
Psychic Detective: series volume 4 - Orgel
the amazing Spider-Man versus The Kingpin
Burai Hachigyoku no Yuushi Densetsu
Android Assault - the revenge of Bari-Arm
World Cup: 1994
Arcus: 1, 2, and 3
3x3 Eyes (AKA Seimaden Setsu)
Dungeon Master: 2 - The Legend of SkullKeep