Apparently, before there was Turtle Rock Studios and Left 4 Dead, there was Zombie City - a mod made for Counter-Strike: Source and Condition Zero.
It's not unusual for mods to eventually become full-fledged and successful games. Two of the most successful online games right now, League of Legends and DOTA 2, first got their starts as mods for Warcraft III: The Frozen Throne. Even Counter-Strike initially started life as a mod for Half-Life before becoming its own game that supported mods that later evolved to a whole bunch of new video games as well. But, what's interesting here is this is arguably the first time we've gotten confirmation that Left 4 Dead actually started as a mod for Counter-Strike under a different name.
Tyler McViker revealed on YouTube what he describes is the early makings of Left 4 Dead. The five-minute video is a brief history of Left 4 Dead and how it went from a map called Zombie City for Counter-Strike: Source and later, Condition Zero, to Left 4 Dead. More importantly, his reveal comes with a pretty interesting reveal - you can download and play Zombie City on Counter-Strike: Source.
Of course, we won't be leaking the info on this article ourselves because, well, that's the law. But, we can confirm the mod is out there and people are playing it already.
It's unclear if McViker himself is the source of the Zombie City leak or if someone else leaked it online. However, from what we can tell, Zombie City is nowhere near a complete game. Instead of fighting zombies with an AI Director possessing a sadistic sense of humor, it's a four-player co-op shooter that pits you against counter-terrorists who refuse to use guns for some reason. Basically, your goal is to make it to the other end of the map alive amidst an onslaught of counter-terrorists. It's a very rudimentary mod that could very well have been the original concept Turtle Rock pitched to Valve before it was greenlit and turned into Left 4 Dead.
When it comes to video game leaks, this is right up there among the biggest of them. We're just somewhat thankful this came out over a decade after Left 4 Dead hit the market. Otherwise, this would've been devastating to Turtle Rock.
Also, it gives us a look at what's easily the most influential multiplayer FPS of all time; if Left 4 Dead can look this bad in development, then there's no need to worry about Grand Theft Auto 6.