Windows

Penumbra: Black Plague

The game's install directory includes a password-protected self-extracting archive by the name super_secret.exe. The password for it, xor451, is shown when the game is completed with all 10 secret artifacts founds. The file includes concept art, desktop backgrounds and a behind-the-scenes movie.

The password can also be used at Swanson's computer when opening the file schmup.exe (in-game) to play a space shooter.