Situation Outbreak is an Orange Box mod about the impending zombie apocalypse. Armed with nothing but a 9mm and a pair of brass knuckles, you must do whatever it takes to survive against the thousands of zombies that used to be your friends and neighbors. The cost of failure is nothing less than your free will. There are no heroes. No single person can save the world and there are not enough bullets to go around. The only thing left to do is to kill the damned, hoping that you don’t end up like them.
I know they're a little hard to make out in this particular screenshot (they dissipate so quickly when they spawn that it is hard to capture a group of them in a single frame!), but SO now has its own custom rain drop particles! Mappers, all you have to do is create a func_precipitation brush entity and the code will do the rest. A small addition, but I nice little effect, I think. =)