vs. Monsters is a 20 page PDF created in 24 hours as part of an exercise. Can you create a roleplaying game in 24 hours?
This game of monster killing in 19th Century America is, in the author's opinion, a failed attempt at a 24 hour game. There are some interesting elements to the design and anyone with an interest in game design will find the contents informative.
If you've ever wanted to design your own game you should give this a look and then attempt your own 24 hour game. --publisher's description.
The game was later expanded into the Deluxe Edition.