High Quality Content by WIKIPEDIA articles! Day of Defeat: Source is a team-based first-person shooter multiplayer video game developed by Valve Corporation. Set in World War II, the game is an updated version of Day of Defeat, moving from the GoldSrc engine used by its predecessor to the Source engine. The game was released for Microsoft Windows on 26 September 2005, distributed through Valve's online content delivery service Steam. Retail distribution of the game was handled by Electronic Arts.