There have been quite a few video game leaks over the past few months, and a recent one shows footage from an early prototype of Left 4 Dead, giving some idea of how the game would have looked at the start of its development cycle. What many would consider one of the most influential zombie games of all time, up there with such contemporaries as Dead Rising, Valve's 2008 co-op shooter has become a classic, winning several awards and accolades from fans and critics alike.

With retro 90s FPS Blood having its source code leaked recently, not to mention the leak for the 2001 build of Duke Nukem Forever being made available to download, it seems many are keen to go behind the scenes of some older releases to see what made them tick. Of course, having access to the official code is one thing, but knowing what to do with it is another. For a lot of gamers, it's just an interesting window into how their favorites titles were made, and in some cases, it gives insight into how a game may have begun its life.

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In a recent post on Twitter by user Wolfcl0ck1, as spotted by DSO Gaming, a video from a Counter-Strike map simply called "Zombie_City" shows a prototype of what would eventually become known as Left 4 Dead. The 10-minute footage shows the player running around a texture-less map as they shoot terrorist-looking enemies labelled as zombies. According to the leaker, this map would have been initially designed by Valve itself or maybe even Turtle Rock Studios, who initially began working on the game in 2005. The map is available to download for anyone who's interested in giving it a try.

For a lot of fans, it's hard to imagine that Left 4 Dead will be turning 15 this year, along with some other classics like Fable 2, Fallout 3, and Gears of War 2. At a time when the zombie genre was at its peak, the L4D series was a phenomenal success, combining high-octane action with cooperative play that didn't get sidetracked by a complicated narrative. Although Back 4 Blood is considered a spiritual successor, for many, it didn't quite hit the mark that Left 4 Dead did.

It's also another example of how Valve's early success lay in video game development. Starting with the first Half-Life in 1998, the Washington-based studio had hit after hit within the first decade or so of its life. These days, the company is known largely for its lucrative Steam client, but many still recall the days of yore when the developer had a knack for creating quality titles.

Left 4 Dead was released in 2008 for PC and Xbox 360.

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Source: DSO Gaming, Twitter, Game Banana