Hatred 4 Dead

Hatred's civilians, cops and soldiers are gone. In their place are Left 4 Dead 2's common infected, with the real L4D2 bodies, skins, animations, groans and screams, loaded straight from your own copy of Left 4 Dead 2 every time you play.

• They don't run away. The infected stand around moaning until they see you or hear your gunfire. Then they scream and sprint at you in packs, a touch faster than you can sprint, and claw you when they get close. Jump in a car and they chase that too.
• Shove them back. Your melee (F) is L4D2's shove: infected in front of you get knocked back and stagger.
• Hordes. Step out of the house and the first horde hits: the L4D2 "incoming" scream, then every infected nearby charges. More hordes come every few minutes.
• Horde music. When a big pack is chasing you, L4D2's horde drums kick in.
• Ragdolls and executions. Shot infected crumple and flop with Hatred's own ragdoll physics, crawl when wounded, and show up in Hatred's close-up executions.
• Who becomes what. Civilians turn into L4D2 street infected, men and women in their everyday clothes. Cops become infected police, and soldiers become infected National Guard. Infected never shoot, but the guns they drop are yours to take.

Single player. You need both Hatred and Left 4 Dead 2 installed. Nothing from either game is copied: the mashup reads L4D2's files from your own install while you play.

Credits: MinHook by Tsuda Kageyu (BSD 2-clause), used to hook into Hatred.