Prodod is a third party Day of Defeat: Source mod that builds on the foundation set down by DOD:S. Various key values from DOD:S have been changed to better suit the competitive community, as well as correct certain things in the game that Valve has consistently stated they will not ever address.
This is a self installer for the game. Just run the installer and click on desktop icon to play the game. Your game will always stay current to the files...