CO-OP CAMPAIGNS
Borderlands 1/2/TPS
Daikatana
Dead Island
Dead Rising
Dead Rising 2 (Off the Record)
Doom 1/2
Doom 3
Dying Light
E.Y.E Divine Cybermancy
F.E.A.R.
Grand Theft Auto V
Grim Dawn
Half-Life/Opposing Force/Blue Shift (Sven Co-op/modded op4)
Half-Life: Decay
Half-Life 2 + EPs (Synergy/Obsidian Conflict)
Lost Planet 2
Path of Exile
Portal 2
Postal Redux
Postal 2
PULSAR: Lost Colony
Quake
Quake 4
Resident Evil 5
Resident Evil 6
Risk of Rain
Serious Sam TFE/TSE/BFE
System Shock 2
Terraria
The Red Solstice
Touhou Diablo
Trine 2
Warcraft 3
Warhammer 40k - Dawn of War 2

CO-OP REPLAYABLE
Alien Swarm: Reactive Drop
Age of Empires/Mythology
Brainbread 2
Call of Duty: Zombies
Dungeons Defenders
Earth Defence Force 4.1
Garry's Mod (the non-shit game modes)
Killing Floor
Killing Floor 2
Left4Dead
Left4Dead 2
Minecraft (with mods)
No More Room in Hell
Obsidian Conflict
OpenRA (Red Alert, Red Alert 2, Tiberian Dawn)
ORION: Prelude
Payday: The Heist
Payday 2
Starcraft 2 (custom games)
Team Fortress 2 - Mann vs. Machine
UNLOVED (standalone)
Warhammer 40k - Dawn of War (+expansions)
Warhammer: End Times - Vermintide
Zenzizenzic
Zombie Army Trilogy

DOOM WADS
Bagel Horde
Epic2
Psychophobia
Stronghold
Unloved

HALF-LIFE MODS
Afraid of Monsters
Brainbread
Natural Selection
Master Sword Continued
Sven Co-op

PVP
Natural Selection 2
Quake 3 Arena
Rising Storm
Team Fortress 2 Vintage

MMO
Planetside 2
World of Warcraft

EMULATED & ARCADE
Mario Party series