Tough Terry is a simple First Person Shooter, that was created for a Raycasting contest. The contest's goal was to create a game similar to Wolfenstein 3D or Doom.
You can download the game here.
The game is a 'Wolfenstein style game', which means that the map does consist of a simple tileset only, where each field is either walkable or not. In contrast to Wolfenstein 3D, there are floor and ceiling textures in the game. The game does require a lot of CPU power, because each horicontal ray has to be calculated separately.
The game is based on the libraries Allegro and AlMP3. This means that it is possible to play the game under Linux, *BSD and Mac if you compile yourself.