Penumbra: Requiem is a survival horror puzzle developed by Frictional Games. It is the third game in Penumbra series of games.
The game picks right off the end of the last one. Phillip sends an e-mail asking his friend to "Kill them. Kill them all.", after which he takes a hit on the head from someone, knocking him unconscious. The main character sets out to escape from the research complex yet again and stumbles upon the notes of another scientist that was also trapped in the complex.
The game features a highly sophisticated physics engine. This allows interacting with in-game items by moving the mouse instead of pointing at clicking at them. The game features no weapons whatsoever and the only option for the players to avoid getting killed is to run away and hide.
Unlike the previous games, Philip can no longer put items in his inventory, yet he can still move them in the world. There are no clues or the characters thoughts present in the notebook. The players have to find keys to activate a portal that leads the players off the level. These keys are usually placed in hard to get spots and require quite a bit of thinking to get to.
There are two endings present in the game. The ending is chosen by the players themselves and is not affected by the players' actions made throughout the game.