Sega Genesis Multiplayer adapter (Adaptador para 4 jugadores).

No es el adaptador multijugador "oficial" de SEGA, pero son comunes para todas las consolas. Este me llamó la atención porque va empotrado directamente en la consola.

Es el Multiplayer adapter de la marca Electronic Arts. Existen adaptadores similares para casi todas las consolas. 

Los juegos "Multiplayer" para Sega Genesis.
La lista la encontré en internet (ahí está todo o casi todo) y son un montón, desde 1 a 4 jugadores:

Electronics Arts Multiplayera adapter

Official Sega Multitap
ATP Tour
Barclay Shut Up & Jam
Barclay Shut Up & Jam 2
College Football's National Championship, College Football's National Championship II
College Slam
Dino Dini's Soccer
Dragon: The Bruce Lee Story
Fever Pitch Soccer / Head-On Soccer
General Chaos
Gauntlet IV
Ichidant-R
International Rugby
International Superstar Soccer Deluxe
J.League Pro Striker 2, J.League Pro Striker Perfect Edition, Pro Striker Final Stage
Lost Vikings
Mega Bomberman
Micro Machines 2 
Mortal Kombat 3
NBA Action 94
NBA Jam
NBA Jam Tournament Edition
NCAA Final Four Basketball
NFL 95, Prime Time NFL, NFL 98
NFL Quarterback Club, NFL Quarterback Club 96
Olympic Gold
Party Quiz: Mega Q
Pele II
Pepen ga Pengo
Sega Sports 1
Slam Dunk From TV Animation
Tant-R
Tiny Toon Adventures: ACME All-Stars
Ultimate Soccer
Wimbledon
World Championship Soccer II
World Cup USA 94
Worms
WWF Raw
Yuu Yuu Hakusho: Makyoutou Issen

36 Greatest holes (32X)
NFL Quarterback Club (32X)
NBA Jam: Tournament Edition (32X)
WWF Raw (32X)

Dungeon Explorer (Sega CD)
Dynamic Country Club (Sega CD)
Egawa Sguru Super League CD (Sega CD)
NBA Jam (Sega CD)
Gauntlet
NBA Hangtime
Street Racer
Super Skidmarks
Wayne Gretzky
ESPN National Hockey Night (Sega CD)

E.A. Multitap
Australian Rugby League
Bill Walsh College Football, Bill Walsh College Football 95
Coach K College Basketball
College Football USA 96, College Football USA 97
Elitserien 95, Elitserien 96
FIFA International Soccer, FIFA 95, FIFA 96, FIFA 97, FIFA Road to the World Cup 98
General Chaos
IMG International Tennis
Madden NFL 94, Madden NFL 95, Madden NFL 96, Madden NFL 97, Madden NFL 98
NBA Live 95, NBA Live 96, NBA Live 97, NBA Live 98
NBA Showdown
NHL 94, NHL 95, NHL 96, NHL 97, NHL 98
PGA Tour Golf III, PGA European Tour, PGA Tour 96
Rugby World Cup 95
Triple Play 96, Triple Play Gold Edition
Wayne Gretzky

FIFA Soccer 96 (32X)

Bill Walsh College Football (Sega CD)
FIFA International Soccer (Sega CD)
NHL 94 (Sega CD)
Gauntlet IV
NBA Hangtime
Street Racer
Wayne Gretzky
ESPN National Hockey Night (Sega CD)