The HPL Engine is a proprietary game engine developed by Frictional Games, primarily known for its use in the Penumbra series. It is designed to facilitate the creation of atmospheric horror and adventure games, with a strong emphasis on physics-based interactions and environmental puzzles. The engine's capabilities allow for detailed environments and realistic object manipulation, contributing significantly to the immersive and suspenseful gameplay experienced in titles like Penumbra: Overture and Penumbra: Black Plague. Its focus on player agency and emergent gameplay mechanics has made it a distinctive tool for narrative-driven experiences.