A cooperative first-person shooter where four survivors fight through zombie-infested campaigns, emphasizing teamwork, resource management, and replayability.
- Developer: Valve
- Year/Platforms: 2009; PC, Xbox 360 (later Mac/Linux)
- Genre: Co-op FPS
- Core mechanics: AI Director 2.0 dynamic pacing, melee weapons, special infected variety, Versus/Scavenge/Survival modes
- Reception: Praised for co-op design and mod support; continued longevity with community campaigns and updates