1916: Der Unbekannte Krieg is a free indie horror game by students of the Danish Academy of Digital Interactive Entertainment. Set during World War I, you play as a German soldier trying to escape the creatures that hunt you through the narrow, claustrophobic trenches by reaching the ladder at the opposite end of the territory. The creatures hunting you are dinosaurs, and you have no way of fighting them. You just run, using whatever tools you can find in the death-ridden trenches.
The game is ultimately fairly short and simple -- it only takes a few minutes to beat if you know what you're doing -- but odds are it'll take you several attempts before you really start to figure it out. The main criticism I have if that it takes too much trial-and-error to learn the basic mechanics of the game, which may turn people off, but once you understand how things work and what you're supposed to be doing, 1916: Der Unbekannte Krieg is a really tense, heart-pounding experience.