Harrow is an episodic set of "interactive fiction" games. They are text-based and require a Z-code interpreter. The most popular interpreters are Frotz, and Gargoyle. If you're new to text adventure games, here is a very brief guide.
The idea for the game came from IF Quake, and Attack of the Yeti Robot Zombies. Both the games aren't particularly serious, but are linear and short– two qualities that are also a part of Harrow. Some added commands for checking status are health and ammo. You can abbreviate weapon names (rl for rocket launcher, sg for shotgun, etc).
Harrow's first adventure is much more shooting than puzzle-solving. It took about two weeks to write using Inform 7 (16-Jun 2010; 6E59). Due to the random nature of the combat rules and the time constraints of the oxygen tank, it will almost definitely take more than one try to win. There are 21 rooms, 4 different types of enemies, 20 total enemies, and 3 different weapons. Click to download .z5.