It an entity that uses various logistics to spawn random items. This video shows how it spawns items depending on number of players (bot's used insted). It starts lagging because of the fact that alot of entities are spawned at same time in short periods, although periods are configurable for server owner. He can choose between min/max random time in seconds for director to spawn items. Director spawn position works in 3steps. 1st chooses to spawn on predesigned node or in bounds of certain location. 2nd chooses a random point in bounds of entity, this step is skipped if predesigned location is choosed. 3rd step spawns the item itself.
Also in the end of the video you can see panel that allows you to select how many rain/snow particles to have in world in same time for people with low-end computers.
Thats about it. Also keep in mind that Director is not same thing as AI Director in l4d, because my director does not have any ai. Everything is random and precalculated.
(Video should be already processed when this is added to ModDB)