Megadrive/Genesis Multiplayer Mayhem!

Here's the things you need:

Gens Emulator, which supports Kaillera, a server system.

Here's some four-player multiplayer games:

Gauntlet 4
General Chaos
MicroMachines 2 - Turbo Tournament
WWF Raw
Worms

EDIT: Further testing indicates the following:

Only General Chaos totally works on four players.
Gauntlet 4 had some sychronization problems.
Micro Machines works only for two players. The other two players see error screen.
WWF Raw doesnt do anything. None of the buttons doesnt seem to work.
Worms doesnt work with four controllers. The game itself supports 8 players, but only uses two controllers.