Valve’s zombie survival horde shooter Left 4 Dead has been immensely successful, to say the least. It has one sequel itself, but many other have made great games based on its formula since. But like many games, this successful creation of a subgenre may have much humbler beginnings. Specifically, it was originally a Counter-Strike mod, just as Counter Strike itself was originally a Half-Life mod.
YouTuber Tyler McVicker claims that Turtle Rock Studios had ideas for a another game type “on top of that engine”, referring to Counter-Strike: Condition Zero. It’s unclear if this was to be a mode for said game, or a prototype for another standalone game. Either way, one of the maps created for this was called Zombie City. This has the Terrorist team of up to four players face infinitely respawning Counter Terrorist bots that are armed with nothing but a knife.
As mentioned, this started with Condition Zero, but it would see more development on Counter-Strike: Source when that came about. There’s even a new codename of “Terror Strike” to go with it. It even had custom models for a lady character, which will presumably evolve into the Zoey we know from Left 4 Dead today.
All this may not necessarily be surprising to hardcore fans of the game who have found Developer Commentary nodes in Left 4 Dead that said just as much. With that being said, if you wanted to experience what playing this prototype feels like before it finally evolved into its own thing, now you can. A version of this got leaked onto the internet as part of a larger Counter-Strike map source leak.
The Zombie_City map can be downloaded from the modding community site GameBanana, with the specific page linked below. Despite this being the Condition Zero map, it looks like it can be ported directly to Counter-Strike: Source and played from there.