I just got done with another session of Left 4 Dead
with a friend and lo and behold, an option to download the beta of the tools for the game has been released through Steam. What you have here is the ability to create levels and other content for the game. I'm hoping to see some creative mods out there for Left 4 Dead
using the new toolset. The tools did crash on me on load but it is a beta so you're probably going to have a few problems here and there.