Here is a quick adaption of the rules made for a play by post RPG.
Genre: cinematic modern horror. Players: 3-12 (Opening scenes are so brutal)
1. GM supplies general setting of the game, e.g. Teenage Slasher or Suburban Zombie Apocalypse. Everyone creates a character accordingly.
2. List FOUR things that the character is especially GOOD at, such as running, driving, climbing, picking locks, survival in the outdoors, fast talking or decapitating zombies using only a vintage 1940s tea set. The GM must ratify these.
3. List TWO things that the character is especially BAD at, such as swimming, finding their way in the wild, avoiding alcohol, keeping their cool in a fight, or not flipping out in confined spaces. GM ratifies as before.
4. Everyone PM's their name on a piece of paper and gives it to the GM.
5. The GM picks out one name at random. This person is the Survivor. No matter WHAT happens (except see below), this person will survive, so long as he is trying to. Everyone else will die. Without exception. Everyone. The players are not told who the Survivor is.
6. The game proceeds. There are no die rolls. The GM decides the outcome of any situation based on that ONE initial intervention of fate - the selection of the Survivor - and on the Players' selection of things that they are good at and bad at. If the GM wishes, however, he can roll dice in private to see which way a situation goes.
7. Even if a player is fated to die, they can keep that fate from occurring for as long as possible by simply being practical and efficient, as in any other game. If you run away from zombies, you may escape for the moment. Not being the Survivor does not mean that you get randomly hit by a bus within five minutes of starting the game. However, there is no way to tell whether, on any given occasion, you survived because you were the Survivor or because the GM decided that your actions were sufficient to let you escape. The only sure thing is that even the Survivor has to make an effort to survive. The difference is that the Survivor *will always* survive.
8. Because of this, the GM is at liberty (and is positively ENCOURAGED) to mess with the players' heads as much as possible. Every narrow escape is a hint that the person MIGHT be the Survivor, OR is the GM screwing with you to make you THINK that the person might be the Survivor.
THE META RULE
9. The Survivor's immunity to death covers NPC actions ONLY. It does not apply to Players, including the Survivor himself. Thus, any attempt to 'test' who the Survivor is, such as by having a character jump into a pool of lava to see whether he dies or not, or any action that the GM interprets as deliberately suicidal, revokes the Survivor's status for the duration of the test. That is, if you shoot yourself in the head to see whether you will die, you will die, whether you were the Survivor or not. In that event, everyone else will still die. The mantle of Survivor does not pass.
THE OPTIONAL BOO-HOO HE WAS SO NOBLE AND SELFLESS RULE
10. The mantle of Survivor *may* be passed to a new character if the Survivor deliberately sacrifices himself so that others can live. 'You go on! I'll hold the zombies back!' 'But you'll DIE!' 'I know. RUN!' etc etc etc.
PLAY BY POST MODIFICATIONS
11. Players, including the survivor, must respond to a situation within n days (where n is an integer between 1 and 3 (preferably 1)) [this will require constant time discpline by the GM]. After all we all know what happens to people who hesitate in horror movies.
12. If the survivor is killed early on due to 11, a new survivor is chosen if the death happened early on.
13. Only in character actions happen in a thread. Whatever you type without quotation marks your character is assumed to do. In quotation marks is what they say.
14. In combat, your character is limited to 2 lines of talk and 1 line of action (slight lee-way dependent upon resolution word limit will be better).
15. If you are killed/get pregnant/eaten as the horror case may be, stop posting in the thread. If you can't access a computer to post, tough, electrical equipment never works in horror movies anyway.
16. An out of character thread may be created to discuss the game and who the survivor might be, but don't discuss strategy to fight/survive, let the others die, remember it takes time to kill other characters allowing yours to survive that much longer.
*Acknowledge I wasnt the original creator of said rules and go pay homage to the person linked above*