Penumbra: Black Plague

Cheats:

Space shooter mini-game:
While playing the game, access Swanson's computer, and run the program "schmup.exe". Enter "xor451" as a password to play a space shooter mini-game.

Bonus material:
Successfully complete the game with all ten secret artifacts collected to get the password "xor451". Run the "super_secret.exe" file in the game's installation directory, and enter "xor451" as a password when prompted to view concept art, desktop backgrounds, and a video.