An early version of what everyone knows today leaked onto the Internet Left 4 Dead co-op action from Valve and Turtle Rock Studios. The prototype of the game was created based on the games Counter-Strike: Condition Zero and Counter-Strike: Source, on which the developers experimented and tested, for example, the behavior of artificial intelligence.
So it’s no surprise that the video attached below of him playing just shows slightly modified version the aforementioned Counter-Strike: Source. After all, the very name Terror-Strike refers to the origin of the prototype.
You can see one in the video experimental map called Zombie City, which you can even download and try yourself thanks to the work of the moderator with the nickname Wolfcl0ck. However, don’t expect a challenging experience close to the final version of Left 4 Dead. This is more of an interest and an example of the original concept that eventually spawned one of the most famous co-op events.
Source :Indian TV
