CRF filename extension is associated with game engine called Enhanced Dark Engine. The engine powered such games Thief: The Dark Project (1998), Thief II: The Metal Age (2000), or System Shock 2.

CRF files store game data in archive format. The data includes level maps, graphics resources, video files, 3D models, audio files, or textures. The engine, developed by Seana Barrett in 1995, was originally named Dark Engine.