The J-Cart was a special cartridge developed by Codemasters for the Sega Mega Drive (Sega Genesis) console. It held not only the game data but also came with two additional gamepad ports. This effectively allowed four players to play simultaneously without any adapters or workarounds. Its initial release was set in early 1994.
Micro Machines 2: Turbo Tournament also allowed up to eight players to play simultaneously using up to four gamepads, each player using only the D-pad or face buttons.
The J-Cart came relatively late in the life cycle of the console. Thus the number of games that support the J-Cart was limited, and all of them came from Codemasters.