Valve has announced that Left 4 Dead 2 will finally be getting Steam Workshop, a portal that allows easy access to player-developed mod content.
According to the official "To compliment the new access to maps, weapons, and items, we are also creating an expanded scripting tool to allow deeper and more varied experiences inside of Left 4 Dead 2. Similar to the current Mutations, these experiences can be laid on top of existing maps or included with brand new maps. These new style Mutations will also be available from the Steam Workshop.",
Left 4 Dead 2 was released on PC on the 19th November, 2009.